Bug 1470163: Load mathml.css upfront, and remove the concept of on-demand builtin UA sheets. r=heycam

On top of the two depending bugs.

Funny how there's a comment referencing bug 77999.

Differential Revision: https://phabricator.services.mozilla.com/D1750

MozReview-Commit-ID: LCuJROu92bo

dom/base/nsDocument.cpp

@@ -1632,7 +1632,7 @@ nsDocument::~nsDocument()
         Accumulate(Telemetry::CSP_UNSAFE_EVAL_DOCUMENTS_COUNT, 1);
       }
 
-      if (MOZ_UNLIKELY(GetMathMLEnabled())) {
+      if (MOZ_UNLIKELY(mMathMLEnabled)) {
         ScalarAdd(Telemetry::ScalarID::MATHML_DOC_COUNT, 1);
       }
     }
@@ -1695,7 +1695,6 @@ nsDocument::~nsDocument()
   if (mAttrStyleSheet) {
     mAttrStyleSheet->SetOwningDocument(nullptr);
   }
-  // We don't own the mOnDemandBuiltInUASheets, so we don't need to reset them.
 
   if (mListenerManager) {
     mListenerManager->Disconnect();
@@ -1918,7 +1917,6 @@ NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INTERNAL(nsDocument)
 
   // Traverse all our nsCOMArrays.
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mStyleSheets)
-  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mOnDemandBuiltInUASheets)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mPreloadingImages)
 
   for (uint32_t i = 0; i < tmp->mFrameRequestCallbacks.Length(); ++i) {
@@ -2457,7 +2455,6 @@ nsIDocument::ResetStylesheetsToURI(nsIURI* aURI)
     // filled the style set.  (This allows us to avoid calling
     // GetStyleBackendType() too early.)
     RemoveDocStyleSheetsFromStyleSets();
-    RemoveStyleSheetsFromStyleSets(mOnDemandBuiltInUASheets, SheetType::Agent);
     RemoveStyleSheetsFromStyleSets(mAdditionalSheets[eAgentSheet], SheetType::Agent);
     RemoveStyleSheetsFromStyleSets(mAdditionalSheets[eUserSheet], SheetType::User);
     RemoveStyleSheetsFromStyleSets(mAdditionalSheets[eAuthorSheet], SheetType::Doc);
@@ -2472,7 +2469,6 @@ nsIDocument::ResetStylesheetsToURI(nsIURI* aURI)
 
   // Release all the sheets
   mStyleSheets.Clear();
-  mOnDemandBuiltInUASheets.Clear();
   for (auto& sheets : mAdditionalSheets) {
     sheets.Clear();
   }
@@ -2536,13 +2532,6 @@ nsIDocument::FillStyleSet(ServoStyleSet* aStyleSet)
     }
   }
 
-  // Iterate backwards to maintain order
-  for (StyleSheet* sheet : Reversed(mOnDemandBuiltInUASheets)) {
-    if (sheet->IsApplicable()) {
-      aStyleSet->PrependStyleSheet(SheetType::Agent, sheet);
-    }
-  }
-
   AppendSheetsToStyleSet(aStyleSet, mAdditionalSheets[eAgentSheet],
                          SheetType::Agent);
   AppendSheetsToStyleSet(aStyleSet, mAdditionalSheets[eUserSheet],
@@ -4131,43 +4120,6 @@ nsIDocument::RemoveChildNode(nsIContent* aKid, bool aNotify)
              "(maybe somebody called GetRootElement() too early?)");
 }
 
-void
-nsIDocument::EnsureOnDemandBuiltInUASheet(StyleSheet* aSheet)
-{
-  if (mOnDemandBuiltInUASheets.Contains(aSheet)) {
-    return;
-  }
-  AddOnDemandBuiltInUASheet(aSheet);
-}
-
-void
-nsIDocument::AddOnDemandBuiltInUASheet(StyleSheet* aSheet)
-{
-  MOZ_ASSERT(!mOnDemandBuiltInUASheets.Contains(aSheet));
-
-  // Prepend here so that we store the sheets in mOnDemandBuiltInUASheets in
-  // the same order that they should end up in the style set.
-  mOnDemandBuiltInUASheets.InsertElementAt(0, aSheet);
-
-  if (aSheet->IsApplicable()) {
-    // This is like |AddStyleSheetToStyleSets|, but for an agent sheet.
-    if (nsIPresShell* shell = GetShell()) {
-      // Note that prepending here is necessary to make sure that html.css etc.
-      // does not override Firefox OS/Mobile's content.css sheet.
-      //
-      // Maybe we should have an insertion point to match the order of
-      // nsDocumentViewer::CreateStyleSet though?
-      //
-      // FIXME(emilio): We probably should, randomly prepending stuff here is
-      // very prone to subtle bugs, behavior differences...
-      shell->StyleSet()->PrependStyleSheet(SheetType::Agent, aSheet);
-      shell->ApplicableStylesChanged();
-    }
-  }
-
-  NotifyStyleSheetAdded(aSheet, false);
-}
-
 void
 nsIDocument::AddStyleSheetToStyleSets(StyleSheet* aSheet)
 {
@@ -9542,21 +9494,6 @@ nsIDocument::CreateStaticClone(nsIDocShell* aCloneContainer)
           }
         }
       }
-
-      // Iterate backwards to maintain order
-      for (StyleSheet* sheet : Reversed(thisAsDoc->mOnDemandBuiltInUASheets)) {
-        if (sheet) {
-          if (sheet->IsApplicable()) {
-            RefPtr<StyleSheet> clonedSheet =
-              sheet->Clone(nullptr, nullptr, clonedDoc, nullptr);
-            NS_WARNING_ASSERTION(clonedSheet,
-                                 "Cloning a stylesheet didn't work!");
-            if (clonedSheet) {
-              clonedDoc->AddOnDemandBuiltInUASheet(clonedSheet);
-            }
-          }
-        }
-      }
     }
   }
   mCreatingStaticClone = false;
@@ -11761,11 +11698,6 @@ nsDocument::DocAddSizeOfExcludingThis(nsWindowSizes& aWindowSizes) const
   aWindowSizes.mLayoutStyleSheetsSize +=
     SizeOfOwnedSheetArrayExcludingThis(mStyleSheets,
                                        aWindowSizes.mState.mMallocSizeOf);
-  // Note that we do not own the sheets pointed to by mOnDemandBuiltInUASheets
-  // (the nsLayoutStyleSheetCache singleton does).
-  aWindowSizes.mLayoutStyleSheetsSize +=
-    mOnDemandBuiltInUASheets.ShallowSizeOfExcludingThis(
-      aWindowSizes.mState.mMallocSizeOf);
   for (auto& sheetArray : mAdditionalSheets) {
     aWindowSizes.mLayoutStyleSheetsSize +=
       SizeOfOwnedSheetArrayExcludingThis(sheetArray,

dom/base/nsIDocument.h

@@ -836,14 +836,6 @@ public:
     mBidiEnabled = true;
   }
 
-  /**
-   * Check if the document contains (or has contained) any MathML elements.
-   */
-  bool GetMathMLEnabled() const
-  {
-    return mMathMLEnabled;
-  }
-
   void SetMathMLEnabled()
   {
     mMathMLEnabled = true;
@@ -1468,28 +1460,6 @@ public:
    * Style sheets are ordered, most significant last.
    */
 
-  /**
-   * These exists to allow us to on-demand load user-agent style sheets that
-   * would otherwise be loaded by nsDocumentViewer::CreateStyleSet. This allows
-   * us to keep the memory used by a document's rule cascade data (the stuff in
-   * its nsStyleSet's nsCSSRuleProcessors) - which can be considerable - lower
-   * than it would be if we loaded all built-in user-agent style sheets up
-   * front.
-   *
-   * By "built-in" user-agent style sheets we mean the user-agent style sheets
-   * that gecko itself supplies (such as html.css and svg.css) as opposed to
-   * user-agent level style sheets inserted by add-ons or the like.
-   *
-   * This function prepends the given style sheet to the document's style set
-   * in order to make sure that it does not override user-agent style sheets
-   * supplied by add-ons or by the app (Firefox OS or Firefox Mobile, for
-   * example), since their sheets should override built-in sheets.
-   *
-   * TODO We can get rid of the whole concept of delayed loading if we fix
-   * bug 77999.
-   */
-  void EnsureOnDemandBuiltInUASheet(mozilla::StyleSheet* aSheet);
-
   mozilla::dom::StyleSheetList* StyleSheets()
   {
     return &DocumentOrShadowRoot::EnsureDOMStyleSheets();
@@ -3616,7 +3586,6 @@ protected:
 
   void UpdateDocumentStates(mozilla::EventStates);
 
-  void AddOnDemandBuiltInUASheet(mozilla::StyleSheet* aSheet);
   void RemoveDocStyleSheetsFromStyleSets();
   void RemoveStyleSheetsFromStyleSets(
       const nsTArray<RefPtr<mozilla::StyleSheet>>& aSheets,
@@ -4418,7 +4387,6 @@ protected:
   nsCOMPtr<nsIRunnable> mMaybeEndOutermostXBLUpdateRunner;
   nsCOMPtr<nsIRequest> mOnloadBlocker;
 
-  nsTArray<RefPtr<mozilla::StyleSheet>> mOnDemandBuiltInUASheets;
   nsTArray<RefPtr<mozilla::StyleSheet>> mAdditionalSheets[AdditionalSheetTypeCount];
 
   // Member to store out last-selected stylesheet set.

dom/mathml/nsMathMLElement.cpp

@@ -106,25 +106,9 @@ nsMathMLElement::BindToTree(nsIDocument* aDocument, nsIContent* aParent,
     aDocument->RegisterPendingLinkUpdate(this);
   }
 
-  nsIDocument* doc = GetComposedDoc();
-  if (doc) {
-    if (!doc->GetMathMLEnabled()) {
-      // Enable MathML and setup the style sheet during binding, not element
-      // construction, because we could move a MathML element from the document
-      // that created it to another document.
-      auto cache = nsLayoutStylesheetCache::Singleton();
-      doc->SetMathMLEnabled();
-      doc->EnsureOnDemandBuiltInUASheet(cache->MathMLSheet());
-
-      // Rebuild style data for the presshell, because style system
-      // optimizations may have taken place assuming MathML was disabled.
-      // (See nsRuleNode::CheckSpecifiedProperties.)
-      RefPtr<nsPresContext> presContext = doc->GetPresContext();
-      if (presContext) {
-        presContext->
-          PostRebuildAllStyleDataEvent(nsChangeHint(0), eRestyle_Subtree);
-      }
-    }
+  // Set the bit in the document for telemetry.
+  if (nsIDocument* doc = GetComposedDoc()) {
+    doc->SetMathMLEnabled();
   }
 
   return rv;

layout/base/nsDocumentViewer.cpp

@@ -2517,6 +2517,11 @@ nsDocumentViewer::CreateStyleSet(nsIDocument* aDocument)
     styleSet->PrependStyleSheet(SheetType::Agent, sheet);
   }
 
+  sheet = cache->MathMLSheet();
+  if (sheet) {
+    styleSet->PrependStyleSheet(SheetType::Agent, sheet);
+  }
+
   styleSet->PrependStyleSheet(SheetType::Agent, cache->UASheet());
 
   if (nsStyleSheetService* sheetService = nsStyleSheetService::GetInstance()) {