Do not set low priority on background tabs.

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 2015 matching lines @@
   // and intercepts/unintercepts the kernel32 API SetPriorityClass in a
   // background thread. If the UI thread invokes this API just when it is
   // intercepted the stack is messed up on return from the interceptor
   // which causes random crashes in the browser process. Our hack for now
   // is to not invoke the SetPriorityClass API if the dll is loaded.
   if (GetModuleHandle(L"cbstext.dll"))
     return;
 #endif  // OS_WIN
 
   // Notify the child process of background state.
-  Send(new ChildProcessMsg_SetProcessBackgrounded(backgrounded));
+  // TODO(wfh): re-enable this after testing if dropping the priority of
+  // backgrounded tabs is the root cause of http://crbug.com/381820.
+  // Send(new ChildProcessMsg_SetProcessBackgrounded(backgrounded));
 
 #if !defined(OS_WIN)
   // Backgrounding may require elevated privileges not available to renderer
   // processes, so control backgrounding from the process host.
 
   // Windows Vista+ has a fancy process backgrounding mode that can only be set
   // from within the process.
   child_process_launcher_->SetProcessBackgrounded(backgrounded);
 #endif  // !OS_WIN
 }
@@ skipping 278 matching lines @@
 }
 
 void RenderProcessHostImpl::OnDeletedGpuMemoryBuffer(
     gfx::GpuMemoryBufferType type,
     const gfx::GpuMemoryBufferId& id) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
   GpuMemoryBufferImpl::DeletedByChildProcess(type, id, GetHandle());
 }
 
 }  // namespace content