Bug 1013784 - Implement ClearRect for BasicCompositor. r=Cwiiis

gfx/layers/Compositor.h

@@ -311,7 +311,7 @@ public:
   /*
    * Clear aRect on current render target.
    */
-  virtual void ClearRect(const gfx::Rect& aRect) { }
+  virtual void ClearRect(const gfx::Rect& aRect) = 0;
 
   /**
    * Start a new frame.

gfx/layers/basic/BasicCompositor.cpp

@@ -373,6 +373,12 @@ BasicCompositor::DrawQuad(const gfx::Rect& aRect,
   buffer->PopClip();
 }
 
+void
+BasicCompositor::ClearRect(const gfx::Rect& aRect)
+{
+  mRenderTarget->mDrawTarget->ClearRect(aRect);
+}
+
 void
 BasicCompositor::BeginFrame(const nsIntRegion& aInvalidRegion,
                             const gfx::Rect *aClipRectIn,

gfx/layers/basic/BasicCompositor.h

@@ -84,6 +84,8 @@ public:
                         gfx::Float aOpacity,
                         const gfx::Matrix4x4 &aTransform) MOZ_OVERRIDE;
 
+  virtual void ClearRect(const gfx::Rect& aRect) MOZ_OVERRIDE;
+
   virtual void BeginFrame(const nsIntRegion& aInvalidRegion,
                           const gfx::Rect *aClipRectIn,
                           const gfx::Matrix& aTransform,