Bug 828312 patch 11: Don't generate change hints for restyling of later continuations, since the handling of the change hints from the first continuation is required to do the necessary work. r=bzbarsky

This depends on bug 898333 in order to avoid causing:
TEST-UNEXPECTED-FAIL | chrome://mochitests/content/chrome/dom/tests/mochitest/chrome/test_focused_link_scroll.xul | Assertion count 1 is greater than expected range 0-0 assertions.
due to the assertion:
###!!! ASSERTION: Shouldn't be trying to restyle non-elements directly: '!aContent || aContent->IsElement()', file ../../../layout/base/nsStyleChangeList.cpp, line 62

The assertion count change in layout/generic/crashtests/571995.xhtml is
expected because it changes us from having 7 of:
###!!! ASSERTION: Shouldn't be trying to restyle non-elements directly: '!aContent || aContent->IsElement()', file ../../../layout/base/nsStyleChangeList.cpp, line 62
with the stack:
  mozilla::ElementRestyler::CaptureChange(nsStyleContext*, nsStyleContext*, nsChangeHint) [layout/base/nsChangeHint.h:191]
  mozilla::ElementRestyler::RestyleSelf(nsRestyleHint) [layout/base/RestyleManager.cpp:2304]
to only having one.  This is expected since this patch changes
RestyleSelf to only call CaptureChange for the first continuation or
block-in-inline sibling.

layout/base/RestyleManager.cpp

@@ -1923,14 +1923,16 @@ RestyleManager::ReparentStyleContext(nsIFrame* aFrame)
 
       // Make sure to call CalcStyleDifference so that the new context ends
       // up resolving all the structs the old context resolved.
-      DebugOnly<nsChangeHint> styleChange =
-        oldContext->CalcStyleDifference(newContext, nsChangeHint(0));
-      // The style change is always 0 because we have the same rulenode and
-      // CalcStyleDifference optimizes us away.  That's OK, though:
-      // reparenting should never trigger a frame reconstruct, and whenever
-      // it's happening we already plan to reflow and repaint the frames.
-      NS_ASSERTION(!(styleChange & nsChangeHint_ReconstructFrame),
-                   "Our frame tree is likely to be bogus!");
+      if (!copyFromContinuation) {
+        DebugOnly<nsChangeHint> styleChange =
+          oldContext->CalcStyleDifference(newContext, nsChangeHint(0));
+        // The style change is always 0 because we have the same rulenode and
+        // CalcStyleDifference optimizes us away.  That's OK, though:
+        // reparenting should never trigger a frame reconstruct, and whenever
+        // it's happening we already plan to reflow and repaint the frames.
+        NS_ASSERTION(!(styleChange & nsChangeHint_ReconstructFrame),
+                     "Our frame tree is likely to be bogus!");
+      }
 
       aFrame->SetStyleContext(newContext);
 
@@ -1986,7 +1988,7 @@ RestyleManager::ReparentStyleContext(nsIFrame* aFrame)
             // Make sure to call CalcStyleDifference so that the new
             // context ends up resolving all the structs the old context
             // resolved.
-            styleChange =
+            DebugOnly<nsChangeHint> styleChange =
               oldExtraContext->CalcStyleDifference(newExtraContext,
                                                    nsChangeHint(0));
             // The style change is always 0 because we have the same
@@ -2112,7 +2114,6 @@ ElementRestyler::ElementRestyler(ParentContextFromChildFrame,
 void
 ElementRestyler::CaptureChange(nsStyleContext* aOldContext,
                                nsStyleContext* aNewContext,
-                               nsIFrame* aContinuation, // TEMPORARY (until bug 828312 patch 11)
                                nsChangeHint aChangeToAssume)
 {
   // Check some invariants about replacing one style context with another.
@@ -2138,7 +2139,7 @@ ElementRestyler::CaptureChange(nsStyleContext* aOldContext,
   NS_UpdateHint(ourChange, aChangeToAssume);
   if (NS_UpdateHint(mHintsHandled, ourChange)) {
     if (!(ourChange & nsChangeHint_ReconstructFrame) || mContent) {
-      mChangeList->AppendChange(aContinuation, mContent, ourChange);
+      mChangeList->AppendChange(mFrame, mContent, ourChange);
     }
   }
   NS_UpdateHint(mHintsNotHandledForDescendants,
@@ -2197,15 +2198,9 @@ ElementRestyler::Restyle(nsRestyleHint aRestyleHint)
 
     // TEMPORARY (until bug 918064):  Call RestyleSelf for each
     // continuation or block-in-inline sibling.
-    nsChangeHint hintsHandled = mHintsHandled;
 
     for (nsIFrame* f = mFrame; f;
          f = GetNextContinuationWithSameStyle(f, oldContext)) {
-      // restore for each continuation, since we need the change hint
-      // posted for each continuation and failing to restore would
-      // suppress that.
-      mHintsHandled = hintsHandled;
-
       RestyleSelf(f, aRestyleHint);
     }
   }
@@ -2380,11 +2375,18 @@ ElementRestyler::RestyleSelf(nsIFrame* aSelf, nsRestyleHint aRestyleHint)
     if (!copyFromContinuation) {
       TryStartingTransition(mPresContext, aSelf->GetContent(),
                             oldContext, &newContext);
+
+      CaptureChange(oldContext, newContext, assumeDifferenceHint);
     }
 
-    CaptureChange(oldContext, newContext, aSelf, assumeDifferenceHint);
     if (!(mHintsHandled & nsChangeHint_ReconstructFrame)) {
-      // if frame gets regenerated, let it keep old context
+      // If the frame gets regenerated, let it keep its old context,
+      // which is important to maintain various invariants about
+      // frame types matching their style contexts.
+      // Note that this check even makes sense if we didn't call
+      // CaptureChange because of copyFromContinuation being true,
+      // since we'll have copied the existing context from the
+      // previous continuation, so newContext == oldContext.
       aSelf->SetStyleContext(newContext);
     }
   }
@@ -2422,8 +2424,7 @@ ElementRestyler::RestyleSelf(nsIFrame* aSelf, nsRestyleHint aRestyleHint)
     MOZ_ASSERT(newExtraContext);
 
     if (oldExtraContext != newExtraContext) {
-      CaptureChange(oldExtraContext, newExtraContext, aSelf,
-                    assumeDifferenceHint);
+      CaptureChange(oldExtraContext, newExtraContext, assumeDifferenceHint);
       if (!(mHintsHandled & nsChangeHint_ReconstructFrame)) {
         aSelf->SetAdditionalStyleContext(contextIndex, newExtraContext);
       }

layout/base/RestyleManager.h

@@ -336,7 +336,6 @@ private:
    */
   void CaptureChange(nsStyleContext* aOldContext,
                      nsStyleContext* aNewContext,
-                     nsIFrame* aContinuation, // TEMPORARY (until bug 828312 patch 11)
                      nsChangeHint aChangeToAssume);
 
   /**

layout/generic/crashtests/crashtests.list

@@ -389,7 +389,7 @@ load 570160.html
 load 570289-1.html
 load 571618-1.svg
 asserts(1) load 571975-1.html # bug 574889
-asserts(7) load 571995.xhtml # 761848
+asserts(1) load 571995.xhtml # 761848
 load 574958.xhtml
 asserts(0-4) load 578977.html # bug 757305
 load 580504-1.xhtml