Control process backgrounding from within the child process on Windows.

Windows has a fancy backgrounding mode which lowers IO priority.
Sadly it can only be set from within the process to be backgrounded.
So add a new ChildProcessMsg to tell child processes when they should
enter and leave background mode.

This reduces glitching during background tab load. This should only be
landed along with https://codereview.chromium.org/298253004/ which
removes backgrounding for active audio tabs.

I expect this will reduce CPU and I/O load significantly for background
processes which will lead to power savings.

This is only done on Windows since ChromeOS / Linux require privileges
only available to the browser process for setting background mode.

BUG=362294
TEST=Play audio. Load background tabs. Observe less/no glitching.
R=jam@chromium.org, luken@chromium.org, nasko@chromium.org

Review URL: https://codereview.chromium.org/305533006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@274071 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/renderer_host/render_process_host_chrome_browsertest.cc

@@ -252,7 +252,9 @@ IN_PROC_BROWSER_TEST_F(ChromeRenderProcessHostTest, ProcessPerTab) {
 
 // We don't change process priorities on Mac or Posix because the user lacks the
 // permission to raise a process' priority even after lowering it.
-#if defined(OS_WIN) || defined(OS_LINUX)
+// TODO(dalecurtis): Reenable this on Windows after figuring out how to reliably
+// wait for the renderer process to process IPC messages.
+#if defined(OS_LINUX)
 IN_PROC_BROWSER_TEST_F(ChromeRenderProcessHostTest, Backgrounding) {
   if (!base::Process::CanBackgroundProcesses()) {
     LOG(ERROR) << "Can't background processes";

content/browser/renderer_host/render_process_host_impl.cc

@@ -1973,9 +1973,16 @@ void RenderProcessHostImpl::SetBackgrounded(bool backgrounded) {
   // is to not invoke the SetPriorityClass API if the dll is loaded.
   if (GetModuleHandle(L"cbstext.dll"))
     return;
-#endif  // OS_WIN
 
+  // Windows Vista+ has a fancy process backgrounding mode that can only be set
+  // from within the process.  So notify the child process of background state.
+  Send(new ChildProcessMsg_SetProcessBackgrounded(backgrounded));
+#else
+
+  // Backgrounding may require elevated privileges not available to renderer
+  // processes, so control backgrounding from the process host.
   child_process_launcher_->SetProcessBackgrounded(backgrounded);
+#endif  // OS_WIN
 }
 
 void RenderProcessHostImpl::OnProcessLaunched() {
@@ -1992,7 +1999,7 @@ void RenderProcessHostImpl::OnProcessLaunched() {
       return;
     }
 
-    child_process_launcher_->SetProcessBackgrounded(backgrounded_);
+    SetBackgrounded(backgrounded_);
   }
 
   // NOTE: This needs to be before sending queued messages because

content/child/child_thread.cc

@@ -441,6 +441,10 @@ bool ChildThread::OnMessageReceived(const IPC::Message& msg) {
     IPC_MESSAGE_HANDLER(ChildProcessMsg_GetChildProfilerData,
                         OnGetChildProfilerData)
     IPC_MESSAGE_HANDLER(ChildProcessMsg_DumpHandles, OnDumpHandles)
+#if defined(OS_WIN)
+    IPC_MESSAGE_HANDLER(ChildProcessMsg_SetProcessBackgrounded,
+                        OnProcessBackgrounded)
+#endif
 #if defined(USE_TCMALLOC)
     IPC_MESSAGE_HANDLER(ChildProcessMsg_GetTcmallocStats, OnGetTcmallocStats)
 #endif
@@ -549,4 +553,10 @@ void ChildThread::EnsureConnected() {
   base::KillProcess(base::GetCurrentProcessHandle(), 0, false);
 }
 
+#if defined(OS_WIN)
+void ChildThread::OnProcessBackgrounded(bool background) {
+  base::Process::Current().SetProcessBackgrounded(background);
+}
+#endif
+
 }  // namespace content

content/child/child_thread.h

@@ -194,6 +194,9 @@ class CONTENT_EXPORT ChildThread
   void OnSetProfilerStatus(tracked_objects::ThreadData::Status status);
   void OnGetChildProfilerData(int sequence_number);
   void OnDumpHandles();
+#if defined(OS_WIN)
+  void OnProcessBackgrounded(bool background);
+#endif
 #ifdef IPC_MESSAGE_LOG_ENABLED
   void OnSetIPCLoggingEnabled(bool enable);
 #endif

content/common/child_process_messages.h

@@ -111,6 +111,12 @@ IPC_MESSAGE_CONTROL1(ChildProcessMsg_GetChildHistogramData,
 // Sent to child processes to dump their handle table.
 IPC_MESSAGE_CONTROL0(ChildProcessMsg_DumpHandles)
 
+#if defined(OS_WIN)
+// Sent to child processes to tell them to enter or leave background mode.
+IPC_MESSAGE_CONTROL1(ChildProcessMsg_SetProcessBackgrounded,
+                     bool /* background */)
+#endif
+
 #if defined(USE_TCMALLOC)
 // Sent to child process to request tcmalloc stats.
 IPC_MESSAGE_CONTROL0(ChildProcessMsg_GetTcmallocStats)