Revert of Revert "[Mac] Reland r276808 Use a native MessagePump instead of a MessagePumpDefault"

base/message_loop/message_loop.cc

Index: base/message_loop/message_loop.cc
diff --git a/base/message_loop/message_loop.cc b/base/message_loop/message_loop.cc
index dd1a393ab08633514df9d6d021a1be7ff4dbd23f..ccece4d38ca1d4acb3d9810b9eb7ba9d646a58a4 100644
--- a/base/message_loop/message_loop.cc
+++ b/base/message_loop/message_loop.cc
@@ -229,6 +229,14 @@
 #define MESSAGE_PUMP_UI scoped_ptr<MessagePump>(new MessagePumpForUI())
 #endif
 
+#if defined(OS_MACOSX)
+  // Use an OS native runloop on Mac to support timer coalescing.
+  #define MESSAGE_PUMP_DEFAULT \
+      scoped_ptr<MessagePump>(new MessagePumpCFRunLoop())
+#else
+  #define MESSAGE_PUMP_DEFAULT scoped_ptr<MessagePump>(new MessagePumpDefault())
+#endif
+
   if (type == MessageLoop::TYPE_UI) {
     if (message_pump_for_ui_factory_)
       return message_pump_for_ui_factory_();
@@ -243,7 +251,7 @@
 #endif
 
   DCHECK_EQ(MessageLoop::TYPE_DEFAULT, type);
-  return scoped_ptr<MessagePump>(new MessagePumpDefault());
+  return MESSAGE_PUMP_DEFAULT;
 }
 
 void MessageLoop::AddDestructionObserver(