Bug 1022612. Part 32: Remove nsDisplayItem::SetVisibleRegionOnLayer. r=mattwoodrow

It is no longer called because FrameLayerBuilder always sets the visible
regions on layers now.

--HG--
extra : rebase_source : b6c375fbbaeb79e7332cb55bdda9943bc1ee7f3c

layout/base/nsDisplayList.h

@@ -1367,11 +1367,6 @@ public:
     }
   }
 
-  // If we return false here it means that if this item creates a layer then
-  // ProcessDisplayItems will not set the visible region on the layer. The item
-  // should set the visible region, usually in BuildContainerLayer.
-  virtual bool SetVisibleRegionOnLayer() { return true; }
-
   bool IsInFixedPos() { return mInFixedPos; }
 
 protected:
@@ -2635,12 +2630,6 @@ public:
     return &mList;
   }
   virtual nsDisplayList* GetChildren() MOZ_OVERRIDE { return &mList; }
-  /**
-   * All our subclasses BuildLayers call
-   * FrameLayerBuilder::BuildContainerLayerFor, which
-   * sets the visible region of the layer correctly.
-   */
-  virtual bool SetVisibleRegionOnLayer() { return false; }
 
   virtual int32_t ZIndex() const MOZ_OVERRIDE
   {