Honor --gpu-switching=force_discrete to always stay on discrete GPU.

ui/gl/gpu_switching_manager.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/gpu_switching_manager.h"
 
 #include "base/logging.h"
 
 namespace gfx {
 
@@ skipping 16 matching lines @@
 void GpuSwitchingManager::ForceUseOfDiscreteGpu() {
   gpu_switching_option_.clear();
   gpu_switching_option_.push_back(PreferDiscreteGpu);
 }
 
 GpuPreference GpuSwitchingManager::AdjustGpuPreference(
     GpuPreference gpu_preference) {
   if (gpu_switching_option_.size() == 0)
     return gpu_preference;
   DCHECK_EQ(gpu_switching_option_.size(), 1u);
+#if defined(OS_MACOSX)
+  // Create a pixel format that lasts the lifespan of Chrome, so Chrome
+  // stays on the discrete GPU.
+  if (gpu_switching_option_[0] == PreferDiscreteGpu)
+    GLContextCGL::ForceUseOfDiscreteGPU();
+#endif  // OS_MACOSX
   return gpu_switching_option_[0];
 }
 
 }  // namespace gfx
+