cc: Fix data race in cc::TaskState::IsFinished.

cc/raster/tile_task.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/tile_task.h"
 
 #include "base/logging.h"
 
 namespace cc {
 
 TileTask::TileTask(bool supports_concurrent_execution)
-    : supports_concurrent_execution_(supports_concurrent_execution) {}
+    : supports_concurrent_execution_(supports_concurrent_execution),
+      did_complete_(false) {}
 
 TileTask::TileTask(bool supports_concurrent_execution,
                    TileTask::Vector* dependencies)
     : supports_concurrent_execution_(supports_concurrent_execution),
-      dependencies_(std::move(*dependencies)) {}
+      dependencies_(std::move(*dependencies)),
+      did_complete_(false) {}
 
-TileTask::~TileTask() {}
+TileTask::~TileTask() {
+  DCHECK(did_complete_);
+}
+
+void TileTask::DidComplete() {
+  DCHECK(!did_complete_);
+  did_complete_ = true;
+}
+
+bool TileTask::HasCompleted() const {
+  return did_complete_;
+}
 
 }  // namespace cc