content: Remove base::WaitableEvent from ChildIOSurfaceManager.

content/child/child_io_surface_manager_mac.h

Index: content/child/child_io_surface_manager_mac.h
diff --git a/content/child/child_io_surface_manager_mac.h b/content/child/child_io_surface_manager_mac.h
index fea9214a69a7f202d0c83ff7fd87901558a11558..6160d5361174f91c1bd56b730967e7a86dd6b399 100644
--- a/content/child/child_io_surface_manager_mac.h
+++ b/content/child/child_io_surface_manager_mac.h
@@ -8,8 +8,6 @@
 #include "base/mac/scoped_mach_port.h"
 #include "base/macros.h"
 #include "base/memory/singleton.h"
-#include "base/synchronization/waitable_event.h"
-#include "base/threading/platform_thread.h"
 #include "content/common/mac/io_surface_manager.h"
 #include "content/common/mac/io_surface_manager_token.h"
 
@@ -38,10 +36,6 @@ class CONTENT_EXPORT ChildIOSurfaceManager : public IOSurfaceManager {
   // Set the token used when communicating with the Mach service.
   void set_token(const IOSurfaceManagerToken& token) {
     token_ = token;

[dshwang, 2015/08/26 13:07:18]

Don't we need lock? IO thread set it and any thread (e.g. worker, impl) will
read it.
Currently WaitableEvent makes sure visibility between threads, but not anymore.

[reveman, 2015/08/26 14:38:21]

A mutex here would be sad as all other code is thread safe. I think the user of
this API should make sure there's no race. It's currently guaranteed by the fact
that both setting this token and anything that can result in an IOSurface being
acquired is a result of some processing on the same thread.

[Robert Sesek, 2015/08/26 17:51:26]

Can you DCHECK that this is supposed to be called on a current thread, then?

[reveman, 2015/08/26 19:40:33]

As discussed, we can't add a DCHECK for this but I made it more clear by adding
a comment to the header.

-#if !defined(NDEBUG)
-    set_token_thread_id_ = base::PlatformThread::CurrentRef();
-#endif
-    set_token_event_.Signal();
   }
 
  private:
@@ -52,10 +46,6 @@ class CONTENT_EXPORT ChildIOSurfaceManager : public IOSurfaceManager {
 
   base::mac::ScopedMachSendRight service_port_;
   IOSurfaceManagerToken token_;
-#if !defined(NDEBUG)
-  base::PlatformThreadRef set_token_thread_id_;
-#endif
-  base::WaitableEvent set_token_event_;
 
   DISALLOW_COPY_AND_ASSIGN(ChildIOSurfaceManager);
 };