WIP GPU scheduler + delayed activation / tile draw

gpu/command_buffer/service/gpu_preferences.h

Index: gpu/command_buffer/service/gpu_preferences.h
diff --git a/gpu/command_buffer/service/gpu_preferences.h b/gpu/command_buffer/service/gpu_preferences.h
index b7db89f457c24d9f473656b55b5da718f27e7729..64b23596bf578834cd14ea1497078536d68cd494 100644
--- a/gpu/command_buffer/service/gpu_preferences.h
+++ b/gpu/command_buffer/service/gpu_preferences.h
@@ -44,6 +44,9 @@ struct GPU_EXPORT GpuPreferences {
   // Prioritizes the UI's command stream in the GPU process.
   bool ui_prioritize_in_gpu_process = false;
 
+  // Enable the GPU channel scheduler.
+  bool enable_gpu_scheduler = false;
+
   // Disables hardware acceleration of video decode, where available.
   bool disable_accelerated_video_decode = false;