Workaround for Intel 6xxx clear to 0/1 bug

ui/gl/gl_gl_api_implementation.cc

 // 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.
 
 #include "ui/gl/gl_gl_api_implementation.h"
 
 #include <vector>
 
 #include "base/command_line.h"
 #include "base/memory/ptr_util.h"
@@ skipping 405 matching lines @@
   GLenum gl_internal_format = GetInternalFormat(version_.get(), internalformat);
   GLApiBase::glRenderbufferStorageMultisampleFn(
       target, samples, gl_internal_format, width, height);
 }
 
 void RealGLApi::glClearFn(GLbitfield mask) {
   if (!g_null_draw_bindings_enabled)
     GLApiBase::glClearFn(mask);
 }
 
+void RealGLApi::glClearColorFn(GLclampf red,
+                               GLclampf green,
+                               GLclampf blue,
+                               GLclampf alpha) {
+  if (GLContext::GetGLWorkarounds().clear_to_zero_or_one_broken &&
+      (1 == red || 0 == red) && (1 == green || 0 == green) &&
+      (1 == blue || 0 == blue) && (1 == alpha || 0 == alpha)) {
+    if (1 == alpha)
+      alpha = 2;
+    else
+      alpha = -1;
+  }
+  GLApiBase::glClearColorFn(red, green, blue, alpha);
+}
+
 void RealGLApi::glDrawArraysFn(GLenum mode, GLint first, GLsizei count) {
   if (!g_null_draw_bindings_enabled)
     GLApiBase::glDrawArraysFn(mode, first, count);
 }
 
 void RealGLApi::glDrawElementsFn(GLenum mode,
                                  GLsizei count,
                                  GLenum type,
                                  const void* indices) {
   if (!g_null_draw_bindings_enabled)
@@ skipping 66 matching lines @@
 
 DebugGLApi::~DebugGLApi() {}
 
 NoContextGLApi::NoContextGLApi() {
 }
 
 NoContextGLApi::~NoContextGLApi() {
 }
 
 }  // namespace gl