[Mac] Reduce timer CPU use in MessagePumpCFRunLoopBase.

base/message_loop/message_pump_mac.h

Index: base/message_loop/message_pump_mac.h
diff --git a/base/message_loop/message_pump_mac.h b/base/message_loop/message_pump_mac.h
index 14b8377b9086b922eacd82765e54d68ae2ef74fa..6780c47e3de9e079597b0c72dd69f529b7fecd65 100644
--- a/base/message_loop/message_pump_mac.h
+++ b/base/message_loop/message_pump_mac.h
@@ -81,6 +81,8 @@ typedef NSAutoreleasePool AutoreleasePoolType;
 class MessagePumpCFRunLoopBase : public MessagePump {
   // Needs access to CreateAutoreleasePool.
   friend class MessagePumpScopedAutoreleasePool;
+  friend class TestMessagePumpCFRunLoopBase;
+
  public:
   MessagePumpCFRunLoopBase();
   ~MessagePumpCFRunLoopBase() override;
@@ -194,6 +196,10 @@ class MessagePumpCFRunLoopBase : public MessagePump {
 
   base::TimerSlack timer_slack_;
 
+  // True if private API for validating/invalidating CFRunLoopTimers is
+  // available for use.
+  bool can_invalidate_timers_;
+
   // The recursion depth of the currently-executing CFRunLoopRun loop on the
   // run loop's thread.  0 if no run loops are running inside of whatever scope
   // the object was created in.