Bug 1507313 part 1: Convert nsIPresShell::mFrameConstructor into a UniquePtr (rather than an owning raw pointer). r=TYLin

Also, null out its alias mFrameManager before it's deleted.

Differential Revision: https://phabricator.services.mozilla.com/D11945

--HG--
extra : moz-landing-system : lando

layout/base/PresShell.cpp

@@ -747,8 +747,7 @@ PresShell::AccessibleCaretEnabled(nsIDocShell* aDocShell)
 }
 
 nsIPresShell::nsIPresShell()
-    : mFrameConstructor(nullptr)
-    , mViewManager(nullptr)
+    : mViewManager(nullptr)
     , mFrameManager(nullptr)
 #ifdef ACCESSIBILITY
     , mDocAccessible(nullptr)
@@ -892,7 +891,8 @@ PresShell::~PresShell()
   MOZ_ASSERT(mAllocatedPointers.IsEmpty(), "Some pres arena objects were not freed");
 
   mStyleSet = nullptr;
-  delete mFrameConstructor;
+  mFrameManager = nullptr;
+  mFrameConstructor = nullptr;
 
   mCurrentEventContent = nullptr;
 }
@@ -929,9 +929,9 @@ PresShell::Init(nsIDocument* aDocument,
   SetNeedStyleFlush();
 
   // Create our frame constructor.
-  mFrameConstructor = new nsCSSFrameConstructor(mDocument, this);
+  mFrameConstructor = MakeUnique<nsCSSFrameConstructor>(mDocument, this);
 
-  mFrameManager = mFrameConstructor;
+  mFrameManager = mFrameConstructor.get();
 
   // The document viewer owns both view manager and pres shell.
   mViewManager->SetPresShell(this);

layout/base/nsIPresShell.h

@@ -281,7 +281,7 @@ public:
 
   mozilla::ServoStyleSet* StyleSet() const { return mStyleSet.get(); }
 
-  nsCSSFrameConstructor* FrameConstructor() const { return mFrameConstructor; }
+  nsCSSFrameConstructor* FrameConstructor() const { return mFrameConstructor.get(); }
 
   /* Enable/disable author style level. Disabling author style disables the entire
    * author level of the cascade, including the HTML preshint level.
@@ -1743,7 +1743,7 @@ protected:
   nsCOMPtr<nsIDocument>     mDocument;
   RefPtr<nsPresContext>   mPresContext;
   mozilla::UniquePtr<mozilla::ServoStyleSet> mStyleSet;
-  nsCSSFrameConstructor*    mFrameConstructor; // [OWNS]
+  mozilla::UniquePtr<nsCSSFrameConstructor> mFrameConstructor;
   nsViewManager*           mViewManager;   // [WEAK] docViewer owns it so I don't have to
   nsPresArena               mFrameArena;
   RefPtr<nsFrameSelection> mSelection;