Add missing (and remove superfluous) 'explicit' from constructors.

cc/test/fake_layer_tree_host_impl.h

 // Copyright 2012 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_LAYER_TREE_HOST_IMPL_H_
 #define CC_TEST_FAKE_LAYER_TREE_HOST_IMPL_H_
 
 #include "cc/layer_tree_host_impl.h"
 #include "cc/single_thread_proxy.h"
 #include "cc/test/fake_layer_tree_host_impl_client.h"
 
 namespace cc {
 
 class FakeLayerTreeHostImpl : public LayerTreeHostImpl {
  public:
-  FakeLayerTreeHostImpl(Proxy* proxy);
+  explicit FakeLayerTreeHostImpl(Proxy* proxy);
   virtual ~FakeLayerTreeHostImpl();
 
   void forcePrepareToDraw() {
     LayerTreeHostImpl::FrameData frameData;
     prepareToDraw(frameData);
     didDrawAllLayers(frameData);
   }
 
  private:
   FakeLayerTreeHostImplClient client_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TEST_FAKE_LAYER_TREE_HOST_IMPL_H_