Control process backgrounding from within the child process on Windows.

content/child/child_thread.cc

Index: content/child/child_thread.cc
diff --git a/content/child/child_thread.cc b/content/child/child_thread.cc
index 0d2e7e0a34541821c0d4f866c05aa88704e70be2..fef733361d3377374e517c918d070eced2924f84 100644
--- a/content/child/child_thread.cc
+++ b/content/child/child_thread.cc
@@ -440,6 +440,10 @@ 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
@@ -548,4 +552,10 @@ void ChildThread::EnsureConnected() {
   base::KillProcess(base::GetCurrentProcessHandle(), 0, false);
 }
 
+#if defined(OS_WIN)
+void ChildThread::OnProcessBackgrounded(bool background) {
+  base::Process::Current().SetProcessBackgrounded(background);

[nasko, 2014/05/28 23:08:37]

Out of curiosity, does that work from inside the sandbox?

[DaleCurtis, 2014/05/29 00:06:59]

Yup, I've confirmed the cpu, io priorities of the processes backgrounded have
gone from "6 (below normal), normal"  to "4 (idle), very low"

+}
+#endif
+
 }  // namespace content