cc: Acquire worker context lock be calling BindToCurrentThread.

cc/output/output_surface.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/output/output_surface.h"
 
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/single_thread_task_runner.h"
 #include "base/thread_task_runner_handle.h"
@@ skipping 111 matching lines @@
     success = context_provider_->BindToCurrentThread();
     if (success) {
       context_provider_->SetLostContextCallback(base::Bind(
           &OutputSurface::DidLoseOutputSurface, base::Unretained(this)));
       context_provider_->SetMemoryPolicyChangedCallback(
           base::Bind(&OutputSurface::SetMemoryPolicy, base::Unretained(this)));
     }
   }
 
   if (success && worker_context_provider_.get()) {
+    ContextProvider::ScopedContextLock scoped_context(

[ericrk, 2015/08/24 21:00:10]

I think this may just be a naming issue and actually safe, but it seems weird
that we take the lock here before calling "SetupLock" - is SetupLock a misnomer?
comment says it "Sets up a lock so this context can be used from multiple
threads.", but it seems that it just passes the existing lock on to the command
buffer, rather than "setting up" anything.

Out of curiosity, were we hitting an issue that this fixes? if so, does that
mean there were other uses of the lock before we call "setuplock"?

[reveman, 2015/08/25 22:59:59]

Yes, the name of this function is a bit confusing. As I mentioned on the bug, we
might want to move this code out of cc::OutputSurface. Here's a patch that does
that instead:

https://codereview.chromium.org/1317743002

I think that's preferred unless there turns out to be some issues with that
approach.

+        worker_context_provider_.get());
+
     success = worker_context_provider_->BindToCurrentThread();
     if (success)
       worker_context_provider_->SetupLock();
   }
 
   if (!success)
     client_ = NULL;
 
   return success;
 }
@@ skipping 76 matching lines @@
           aggressively_free_resources);
     }
   }
 }
 
 bool OutputSurface::SurfaceIsSuspendForRecycle() const {
   return false;
 }
 
 }  // namespace cc