Allow DrawingBuffer to present to a bitmap.

Source/core/platform/graphics/GraphicsContext3D.h

Index: Source/core/platform/graphics/GraphicsContext3D.h
diff --git a/Source/core/platform/graphics/GraphicsContext3D.h b/Source/core/platform/graphics/GraphicsContext3D.h
index d0f7deb23b021898685f0f9195a60051230efdbb..283f288c22083715e13a802fbb13b226797576c5 100644
--- a/Source/core/platform/graphics/GraphicsContext3D.h
+++ b/Source/core/platform/graphics/GraphicsContext3D.h
@@ -789,6 +789,16 @@ public:
 
     // End GraphicsContext3DImagePacking.cpp functions
 
+    // This is the order of bytes to use when doing a readback.
+    enum ReadbackOrder {
+        ReadbackRGBA,
+        ReadbackSkia
+    };
+
+    // Helper function which does a readback from the currently-bound
+    // framebuffer into a buffer of a certain size with 4-byte pixels.
+    void readBackFramebuffer(unsigned char* pixels, int width, int height, ReadbackOrder, AlphaOp);
+
 private:
     friend class Extensions3D;
 
@@ -804,6 +814,8 @@ private:
     static bool packPixels(const uint8_t* sourceData, DataFormat sourceDataFormat, unsigned width, unsigned height, unsigned sourceUnpackAlignment, unsigned destinationFormat, unsigned destinationType, AlphaOp, void* destinationData, bool flipY);
 
     void paintFramebufferToCanvas(int framebuffer, int width, int height, bool premultiplyAlpha, ImageBuffer*);
+    // Helper function to flip a bitmap vertically.
+    void flipVertically(uint8_t* data, int width, int height);
 
     // Extensions3D support.
     bool supportsExtension(const String& name);
@@ -826,6 +838,7 @@ private:
     HashSet<String> m_requestableExtensions;
     bool m_layerComposited;
     bool m_preserveDrawingBuffer;
+    int m_packAlignment;
 
     enum ResourceSafety {
         ResourceSafetyUnknown,
@@ -843,6 +856,9 @@ private:
 
     GrContext* m_grContext;
     SkAutoTUnref<GrContext> m_ownedGrContext;
+
+    // Used to flip a bitmap vertically.
+    Vector<uint8_t> m_scanline;
 };
 
 } // namespace WebCore