cc: Use compositor context for signal sync token callback.

cc/raster/gpu_raster_buffer_provider.cc

 // Copyright 2014 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/raster/gpu_raster_buffer_provider.h"
 
 #include <stdint.h>
 
 #include <algorithm>
 
@@ skipping 199 matching lines @@
     uint64_t pending_callback_id) const {
   if (!async_worker_context_enabled_)
     return 0;
 
   gpu::SyncToken sync_token =
       resource_provider_->GetSyncTokenForResources(resource_ids);
   uint64_t callback_id = sync_token.release_count();
   DCHECK_NE(callback_id, 0u);
 
   // If the callback is different from the one the caller is already waiting on,
-  // pass the callback through to SignalSinkToken. Otherwise the request is
+  // pass the callback through to SignalSyncToken. Otherwise the request is
   // redundant.
   if (callback_id != pending_callback_id) {
-    // SignalSyncToken is threadsafe, no need for worker context lock.
-    worker_context_provider_->ContextSupport()->SignalSyncToken(sync_token,
-                                                                callback);
+    // Use the compositor context because we want this callback on the impl
+    // thread.
+    compositor_context_provider_->ContextSupport()->SignalSyncToken(sync_token,
+                                                                    callback);
   }
 
   return callback_id;
 }
 
 void GpuRasterBufferProvider::Shutdown() {
   pending_raster_buffers_.clear();
 }
 
 void GpuRasterBufferProvider::PlaybackOnWorkerThread(
@@ skipping 31 matching lines @@
   gl->OrderingBarrierCHROMIUM();
 
   // Generate sync token after the barrier for cross context synchronization.
   gpu::SyncToken resource_sync_token;
   gl->GenUnverifiedSyncTokenCHROMIUM(fence_sync, resource_sync_token.GetData());
   resource_lock->set_sync_token(resource_sync_token);
   resource_lock->set_synchronized(!async_worker_context_enabled_);
 }
 
 }  // namespace cc