Workaround for Intel 6xxx clear to 0/1 bug

ui/gl/gl_gl_api_implementation.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_GL_GL_GL_API_IMPLEMENTATION_H_
 #define UI_GL_GL_GL_API_IMPLEMENTATION_H_
 
 #include <memory>
 #include <vector>
 
@@ skipping 85 matching lines @@
                                              GLsizei width,
                                              GLsizei height) override;
 
   void glRenderbufferStorageMultisampleFn(GLenum target,
                                           GLsizei samples,
                                           GLenum internalformat,
                                           GLsizei width,
                                           GLsizei height) override;
 
   void glClearFn(GLbitfield mask) override;
+  void glClearColorFn(GLclampf red,
+                      GLclampf green,
+                      GLclampf blue,
+                      GLclampf alpha) override;
   void glDrawArraysFn(GLenum mode, GLint first, GLsizei count) override;
   void glDrawElementsFn(GLenum mode,
                         GLsizei count,
                         GLenum type,
                         const void* indices) override;
 
   void glClearDepthFn(GLclampd depth) override;
   void glDepthRangeFn(GLclampd z_near, GLclampd z_far) override;
 
   void InitializeFilteredExtensions();
@@ skipping 50 matching lines @@
 
   // Include the auto-generated part of this class. We split this because
   // it means we can easily edit the non-auto generated parts right here in
   // this file instead of having to edit some template or the code generator.
   #include "gl_bindings_api_autogen_gl.h"
 };
 
 }  // namespace gl
 
 #endif  // UI_GL_GL_GL_API_IMPLEMENTATION_H_