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

content/browser/renderer_host/render_process_host_impl.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.
 
 // Represents the browser side of the browser <--> renderer communication
 // channel. There will be one RenderProcessHost per renderer process.
 
 #include "content/browser/renderer_host/render_process_host_impl.h"
 
 #include <algorithm>
@@ skipping 1063 matching lines @@
     command_line->AppendSwitchASCII(
         switches::kNumRasterThreads,
         base::IntToString(NumberOfRendererRasterThreads()));
   } else {
     command_line->AppendSwitch(switches::kDisableImplSidePainting);
   }
 
   if (IsGpuRasterizationEnabled())
     command_line->AppendSwitch(switches::kEnableGpuRasterization);
 
+  if (IsThreadedGpuRasterizationEnabled())
+    command_line->AppendSwitch(switches::kEnableThreadedGpuRasterization);
+
   int msaa_sample_count = GpuRasterizationMSAASampleCount();
   if (msaa_sample_count > 0) {
     command_line->AppendSwitchASCII(
         switches::kGpuRasterizationMSAASampleCount,
         base::IntToString(msaa_sample_count));
   }
 
   DCHECK_IMPLIES(IsZeroCopyUploadEnabled(), !IsOneCopyUploadEnabled());
   DCHECK_IMPLIES(IsOneCopyUploadEnabled(), !IsZeroCopyUploadEnabled());
   if (IsZeroCopyUploadEnabled())
@@ skipping 1294 matching lines @@
 
 void RenderProcessHostImpl::DecrementWorkerRefCount() {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   DCHECK_GT(worker_ref_count_, 0);
   --worker_ref_count_;
   if (worker_ref_count_ == 0)
     Cleanup();
 }
 
 }  // namespace content