Direct composite canvas background if possible.

public/platform/WebExternalTextureLayer.h

Index: public/platform/WebExternalTextureLayer.h
diff --git a/public/platform/WebExternalTextureLayer.h b/public/platform/WebExternalTextureLayer.h
index 180b81f58aba803db1b9f9b6fe5dadc5ac2632ce..6cd9e94fb94f0e77e75d2f02a2146655722a0f44 100644
--- a/public/platform/WebExternalTextureLayer.h
+++ b/public/platform/WebExternalTextureLayer.h
@@ -55,6 +55,10 @@ public:
     // Sets whether this layer's texture has premultiplied alpha or not. Defaults to true.
     virtual void setPremultipliedAlpha(bool) = 0;
 
+    // Sets whether the texture should be blended with the background color
+    // at draw time. Defaults to false.
+    virtual void setBlendBackgroundColor(bool) = 0;
+
     // Sets whether this context should be rate limited by the compositor. Rate limiting works by blocking
     // invalidate() and invalidateRect() calls if the compositor is too many frames behind.
     virtual void setRateLimitContext(bool) = 0;