Bug 1284888 part 2: Make TextOverflow::WillProcessLines() return a UniquePtr, for stronger lifetime guarantees. r=jfkthame

MozReview-Commit-ID: 7KVsFlxuL9p

--HG--
extra : rebase_source : 13ee634d9a310236f70c30afa0d3c5a798a00194

layout/generic/TextOverflow.cpp

@@ -335,7 +335,7 @@ TextOverflow::TextOverflow(nsDisplayListBuilder* aBuilder,
   // has overflow on that side.
 }
 
-/* static */ TextOverflow*
+/* static */ UniquePtr<TextOverflow>
 TextOverflow::WillProcessLines(nsDisplayListBuilder*   aBuilder,
                                nsIFrame*               aBlockFrame)
 {
@@ -350,7 +350,7 @@ TextOverflow::WillProcessLines(nsDisplayListBuilder*   aBuilder,
     // If the APZ is actively scrolling this, don't bother with markers.
     return nullptr;
   }
-  return new TextOverflow(aBuilder, aBlockFrame);
+  return MakeUnique<TextOverflow>(aBuilder, aBlockFrame);
 }
 
 void

layout/generic/TextOverflow.h

@@ -11,6 +11,7 @@
 #include "nsTHashtable.h"
 #include "mozilla/Attributes.h"
 #include "mozilla/Likely.h"
+#include "mozilla/UniquePtr.h"
 #include "mozilla/WritingModes.h"
 #include <algorithm>
 
@@ -32,8 +33,18 @@ class MOZ_HEAP_CLASS TextOverflow final {
    * Allocate an object for text-overflow processing.
    * @return nullptr if no processing is necessary.  The caller owns the object.
    */
-  static TextOverflow* WillProcessLines(nsDisplayListBuilder*   aBuilder,
-                                        nsIFrame*               aBlockFrame);
+  static UniquePtr<TextOverflow>
+  WillProcessLines(nsDisplayListBuilder* aBuilder,
+                   nsIFrame*             aBlockFrame);
+
+  /**
+   * Constructor, which client code SHOULD NOT use directly. Instead, clients
+   * should call WillProcessLines(), which is basically the factory function
+   * for TextOverflow instances.
+   */
+  TextOverflow(nsDisplayListBuilder* aBuilder,
+               nsIFrame* aBlockFrame);
+
   /**
    * Analyze the display lists for text overflow and what kind of item is at
    * the content edges.  Add display items for text-overflow markers as needed
@@ -59,9 +70,6 @@ class MOZ_HEAP_CLASS TextOverflow final {
   typedef nsTHashtable<nsPtrHashKey<nsIFrame>> FrameHashtable;
 
  private:
-  TextOverflow(nsDisplayListBuilder* aBuilder,
-               nsIFrame* aBlockFrame);
-
   typedef mozilla::WritingMode WritingMode;
   typedef mozilla::LogicalRect LogicalRect;
 

layout/generic/nsBlockFrame.cpp

@@ -6756,8 +6756,8 @@ nsBlockFrame::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
   aBuilder->MarkFramesForDisplayList(this, mFloats, aDirtyRect);
 
   // Prepare for text-overflow processing.
-  UniquePtr<TextOverflow> textOverflow(
-    TextOverflow::WillProcessLines(aBuilder, this));
+  UniquePtr<TextOverflow> textOverflow =
+    TextOverflow::WillProcessLines(aBuilder, this);
 
   // We'll collect our lines' display items here, & then append this to aLists.
   nsDisplayListCollection linesDisplayListCollection;