Created multi-process-friendly PowerMonitor interface.

content/gpu/gpu_main.cc

Index: content/gpu/gpu_main.cc
diff --git a/content/gpu/gpu_main.cc b/content/gpu/gpu_main.cc
index 221361feae2df5fe75e05fa3fe72fc60ca889f83..3b5148497a4a1004bdd39cf0950a0066f12bd7a1 100644
--- a/content/gpu/gpu_main.cc
+++ b/content/gpu/gpu_main.cc
@@ -11,6 +11,7 @@
 #include "base/debug/trace_event.h"
 #include "base/lazy_instance.h"
 #include "base/message_loop.h"
+#include "base/power_monitor/power_monitor.h"
 #include "base/rand_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/stringprintf.h"
@@ -19,6 +20,7 @@
 #include "content/child/child_process.h"
 #include "content/common/gpu/gpu_config.h"
 #include "content/common/gpu/gpu_messages.h"
+#include "content/common/power_monitor_broadcast_source.h"
 #include "content/common/sandbox_linux.h"
 #include "content/gpu/gpu_child_thread.h"
 #include "content/gpu/gpu_process.h"
@@ -169,6 +171,9 @@ int GpuMain(const MainFunctionParams& parameters) {
   delayed_watchdog_enable = true;
 #endif
 
+  PowerMonitorBroadcastSource* power_monitor_source =
+      new PowerMonitorBroadcastSource();
+  base::PowerMonitor power_monitor(power_monitor_source);
   scoped_refptr<GpuWatchdogThread> watchdog_thread;
 
   // Start the GPU watchdog only after anything that is expected to be time
@@ -283,6 +288,9 @@ int GpuMain(const MainFunctionParams& parameters) {
                                                     dead_on_arrival,
                                                     gpu_info,
                                                     deferred_messages.Get());
+
+  child_thread->channel()->AddFilter(power_monitor_source->MessageFilter());

[piman, 2013/07/12 21:09:58]

So, what is meant to happen on Android, where the GpuChildThread is in-process,
created in GpuProcessHost?
Should we avoid creating the PowerMonitorMessageBroadcaster then, assuming the
GPU thread would get notification from the process-wide PowerMonitor directly,
so that we avoid sending messages that have no receiver?

[bajones, 2013/07/13 00:33:20]

That's a good point. I've added a guard on in_browser_process around the
PowerMonitor creation in this file.

[piman, 2013/07/13 00:44:41]

That's not exactly what I had in mind... On Android (or with --single-process)
GpuMain isn't called at all. Instead a GpuChildThread is created from
GpuMainThread in gpu_process_host.cc (from the GpuProcessHost creation). That
one won't have a filter, which is probably ok, since you don't want to forward
the state from the existing PowerMonitor to itself.
However, the GpuProcessHostUIShim will still be created, and with it the
PowerMonitorMessageBroadcaster, which will send the messages when there's no
receiver.

+
   while (!deferred_messages.Get().empty())
     deferred_messages.Get().pop();