Disable rendering when suspending on chrome os

ash/shell.h

Index: ash/shell.h
diff --git a/ash/shell.h b/ash/shell.h
index 155d33947de370ec3634c10be1bb426357eb02b6..b37f284626dc5bf13ad8f851541c0075d378972e 100644
--- a/ash/shell.h
+++ b/ash/shell.h
@@ -380,6 +380,9 @@ class ASH_EXPORT Shell : public SystemModalContainerEventFilterDelegate,
     return display_controller_.get();
   }
 #if defined(OS_CHROMEOS)
+  PowerEventObserver* power_event_observer() {
+    return power_event_observer_.get();
+  }
   TouchTransformerController* touch_transformer_controller() {
     return touch_transformer_controller_.get();
   }