cc: Fix use-after-frees for LayerTreeHostAnimationTest.

cc/trees/task_runner_provider.h

 // Copyright 2015 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.
 
 #ifndef CC_TREES_TASK_RUNNER_PROVIDER_H_
 #define CC_TREES_TASK_RUNNER_PROVIDER_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 21 matching lines @@
 // Useful for assertion checks.
 class CC_EXPORT TaskRunnerProvider {
  public:
   static std::unique_ptr<TaskRunnerProvider> Create(
       scoped_refptr<base::SingleThreadTaskRunner> main_task_runner,
       scoped_refptr<base::SingleThreadTaskRunner> impl_task_runner) {
     return base::WrapUnique(
         new TaskRunnerProvider(main_task_runner, impl_task_runner));
   }
 
+  // TODO(vmpstr): Should these return scoped_refptr to task runners? Many
+  // places turn them into scoped_refptrs. How many of them need to?
   base::SingleThreadTaskRunner* MainThreadTaskRunner() const;
   bool HasImplThread() const;
   base::SingleThreadTaskRunner* ImplThreadTaskRunner() const;
 
   // Debug hooks.
   bool IsMainThread() const;
   bool IsImplThread() const;
   bool IsMainThreadBlocked() const;
 #if DCHECK_IS_ON()
   void SetMainThreadBlocked(bool is_main_thread_blocked);
@@ skipping 55 matching lines @@
   ~DebugScopedSetMainThreadBlocked() {}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(DebugScopedSetMainThreadBlocked);
 };
 #endif
 
 }  // namespace cc
 
 #endif  // CC_TREES_TASK_RUNNER_PROVIDER_H_