ozone: ClientPixmapManager passes VGEM fd from browser to renderer.

content/child/child_io_surface_manager_mac.cc

Index: content/child/child_io_surface_manager_mac.cc
diff --git a/content/child/child_io_surface_manager_mac.cc b/content/child/child_io_surface_manager_mac.cc
index 1e5665afd0afaf05a556c104833c40d8a8879382..6c280606a65451abc9f2a163feaf52e18ece3a99 100644
--- a/content/child/child_io_surface_manager_mac.cc
+++ b/content/child/child_io_surface_manager_mac.cc
@@ -96,9 +96,7 @@ IOSurfaceRef ChildIOSurfaceManager::AcquireIOSurface(int io_surface_id) {
   // A valid token is required to acquire an IOSurface. This will wait for a
   // valid token if one has not yet been set.
   set_token_event_.Wait();
-#if !defined(NDEBUG)
-  DCHECK(!(set_token_thread_id_ == base::PlatformThread::CurrentRef()));
-#endif
+  DCHECK(!set_token_thread_checker_->CalledOnValidThread());

[reveman, 2015/08/18 14:34:27]

this is not the same. you can't use a thread checker to verify that that some
code is called on the wrong thread. it's confusing as a start but also incorrect
as the thread checker is allowed to always return true and this is then broken.
please change it back but use DCHECK_IS_ON instead

[dshwang, 2015/08/18 14:45:50]

How it's different. The implementation is same;
https://code.google.com/p/chromium/codesearch#chromium/src/base/threading/thr...
Keep in mind |set_token_thread_checker_| is created in set_token().

[reveman, 2015/08/18 15:02:38]

if ENABLE_THREAD_CHECKER is false then this is the implementation used:
https://code.google.com/p/chromium/codesearch#chromium/src/base/threading/thr...
and this check will always fail.

[dshwang, 2015/08/18 15:41:44]

ENABLE_THREAD_CHECKER is true if (!defined(NDEBUG) ||
defined(DCHECK_ALWAYS_ON)).
https://code.google.com/p/chromium/codesearch#chromium/src/base/threading/thr...

DCHECK is enabled only if (!defined(NDEBUG) || defined(DCHECK_ALWAYS_ON)).
We check CalledOnValidThread() inside DCHECK, otherwise it's no-op. so I think
it's ok.
WDYT?

   DCHECK(!token_.IsZero());
 
   mach_port_t reply_port;