WebGL GL_RGB emulation to support IOSurfaces on Mac.

third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h

Index: third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h
diff --git a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h
index 5981cd97f34ee6d61e445ea2baf674ca33a2e422..4c51e6c8bc7d2e9987729fe2460164b87df48c0e 100644
--- a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h
+++ b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.h
@@ -158,6 +158,12 @@ public:
     void setIsHidden(bool);
     void setFilterQuality(SkFilterQuality);
 
+    // Indicates that the currently bound framebuffer has internalformat
+    // GL_RGBA, but is emulating GL_RGB. This happens to the backbuffer when the
+    // client requests alpha:False, but GL_RGB textures are unusable because of
+    // driver bugs.
+    bool requiresRGBEmulation();
+
     WebLayer* platformLayer();
 
     WebGraphicsContext3D* context();
@@ -292,6 +298,10 @@ private:
     // Allocate buffer storage to be sent to compositor using either texImage2D or CHROMIUM_image based on available support.
     void deleteChromiumImageForTexture(TextureInfo*);
 
+    // If RGB emulation is required, then the CHROMIUM image must be immediately
+    // cleared after it is bound to a texture.
+    void clearChromiumImageIfNecessary(const TextureInfo&);
+
     // Tries to create a CHROMIUM_image backed texture if
     // RuntimeEnabledFeatures::webGLImageChromiumEnabled() is true. On failure,
     // or if the flag is false, creates a default texture.