Add a command-line flag to enable threaded GPU rasterization.

content/renderer/gpu/render_widget_compositor.cc

 // Copyright (c) 2013 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 "content/renderer/gpu/render_widget_compositor.h"
 
 #include <limits>
 #include <string>
 
 #include "base/command_line.h"
@@ skipping 221 matching lines @@
   settings.max_untiled_layer_size = gfx::Size(max_untiled_layer_width,
                                            max_untiled_layer_height);
 
   settings.gpu_rasterization_msaa_sample_count =
       compositor_deps_->GetGpuRasterizationMSAASampleCount();
   settings.impl_side_painting = compositor_deps_->IsImplSidePaintingEnabled();
   settings.gpu_rasterization_forced =
       compositor_deps_->IsGpuRasterizationForced();
   settings.gpu_rasterization_enabled =
       compositor_deps_->IsGpuRasterizationEnabled();
+  settings.threaded_gpu_rasterization_enabled =
+      compositor_deps_->IsThreadedGpuRasterizationEnabled();
   settings.can_use_lcd_text = compositor_deps_->IsLcdTextEnabled();
   settings.use_distance_field_text =
       compositor_deps_->IsDistanceFieldTextEnabled();
   settings.use_zero_copy = compositor_deps_->IsZeroCopyEnabled();
   settings.use_one_copy = compositor_deps_->IsOneCopyEnabled();
   settings.enable_elastic_overscroll =
       compositor_deps_->IsElasticOverscrollEnabled();
   settings.use_image_texture_target = compositor_deps_->GetImageTextureTarget();
 
   settings.calculate_top_controls_position =
@@ skipping 625 matching lines @@
   widget_->OnSwapBuffersAborted();
 }
 
 void RenderWidgetCompositor::RateLimitSharedMainThreadContext() {
   cc::ContextProvider* provider =
       compositor_deps_->GetSharedMainThreadContextProvider();
   provider->ContextGL()->RateLimitOffscreenContextCHROMIUM();
 }
 
 }  // namespace content