Handle RenderProcessHostImpl::SetBackgrounded on Windows

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 2189 matching lines @@
   // The cbstext.dll loads as a global GetMessage hook in the browser process
   // 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
 
+#if defined(OS_WIN)
+  // Same as below, but bound to an experiment (http://crbug.com/458594)
+  // initially on Windows. Enabled by default in the asbence of field trials to
+  // get coverage on the perf waterfall.
+  base::FieldTrial* trial =
+      base::FieldTrialList::Find("BackgroundRendererProcesses");
+  if (!trial || (trial->group_name() != "Disallow" &&
+                 trial->group_name() != "AllowBackgroundModeFromRenderer")) {
+    child_process_launcher_->SetProcessBackgrounded(backgrounded);
+  }
+#else
+  // Control the background state from the browser process, otherwise the task
+  // telling the renderer to "unbackground" itself may be preempted by other
+  // tasks executing at lowered priority ahead of it or simply by not being
+  // swiftly scheduled by the OS per the low process priority
+  // (http://crbug.com/398103).
+  child_process_launcher_->SetProcessBackgrounded(backgrounded);
+#endif  // OS_WIN
+
   // Notify the child process of background state.
   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
 }
 
 void RenderProcessHostImpl::OnProcessLaunched() {
   // No point doing anything, since this object will be destructed soon.  We
   // especially don't want to send the RENDERER_PROCESS_CREATED notification,
   // since some clients might expect a RENDERER_PROCESS_TERMINATED afterwards to
   // properly cleanup.
   if (deleting_soon_)
     return;
 
@@ skipping 168 matching lines @@
   if (worker_ref_count_ == 0)
     Cleanup();
 }
 
 void RenderProcessHostImpl::GetAudioOutputControllers(
     const GetAudioOutputControllersCallback& callback) const {
   audio_renderer_host()->GetOutputControllers(callback);
 }
 
 }  // namespace content