Fix blits from multisampled renderbuffers to alpha:false WebGL back buffer.

ui/gl/gl_image.h

Index: ui/gl/gl_image.h
diff --git a/ui/gl/gl_image.h b/ui/gl/gl_image.h
index f0d08423a6f1f3206138c8d50b22e87b325bca4b..be3d6f4c3918cf0fb683ac08e4535c18a11849ea 100644
--- a/ui/gl/gl_image.h
+++ b/ui/gl/gl_image.h
@@ -43,6 +43,13 @@ class GL_EXPORT GLImage : public base::RefCounted<GLImage> {
   // It is valid for an implementation to always return false.
   virtual bool BindTexImage(unsigned target) = 0;
 
+  // Bind image to texture currently bound to |target|, forcing the texture's
+  // internal format to the specified one. This is a feature not available on
+  // all platforms. Returns true on success.  It is valid for an implementation
+  // to always return false.
+  virtual bool BindTexImageWithInternalformat(unsigned target,
+                                              unsigned internalformat);
+
   // Release image from texture currently bound to |target|.
   virtual void ReleaseTexImage(unsigned target) = 0;