Remove unused thread.h include in trace_event_impl.h and fix IWUU.

cc/test/fake_external_begin_frame_source.h

 // 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.
 
 #ifndef CC_TEST_FAKE_EXTERNAL_BEGIN_FRAME_SOURCE_H_
 #define CC_TEST_FAKE_EXTERNAL_BEGIN_FRAME_SOURCE_H_
 
 #include <set>
 
 #include "base/cancelable_callback.h"
 #include "base/memory/weak_ptr.h"
+#include "base/threading/non_thread_safe.h"
 #include "cc/scheduler/begin_frame_source.h"
 
 namespace cc {
 
 class FakeExternalBeginFrameSource
     : public BeginFrameSource,
       public NON_EXPORTED_BASE(base::NonThreadSafe) {
  public:
   class Client {
    public:
@@ skipping 27 matching lines @@
   Client* client_ = nullptr;
   bool paused_ = false;
   std::set<BeginFrameObserver*> observers_;
   base::CancelableCallback<void(const BeginFrameArgs&)> begin_frame_task_;
   base::WeakPtrFactory<FakeExternalBeginFrameSource> weak_ptr_factory_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TEST_FAKE_EXTERNAL_BEGIN_FRAME_SOURCE_H_