Cleanup: Pass std::string as const reference if possible

ui/compositor/layer.cc

 // Copyright (c) 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.
 
 #include "ui/compositor/layer.h"
 
 #include <algorithm>
 
 #include "base/auto_reset.h"
 #include "base/command_line.h"
@@ skipping 790 matching lines @@
 void Layer::SetForceRenderSurface(bool force) {
   if (force_render_surface_ == force)
     return;
 
   force_render_surface_ = force;
   cc_layer_->SetForceRenderSurface(force_render_surface_);
 }
 
 class LayerDebugInfo : public base::trace_event::ConvertableToTraceFormat {
  public:
-  explicit LayerDebugInfo(std::string name) : name_(name) { }
+  explicit LayerDebugInfo(const std::string& name) : name_(name) {}
   void AppendAsTraceFormat(std::string* out) const override {
     base::DictionaryValue dictionary;
     dictionary.SetString("layer_name", name_);
     base::JSONWriter::Write(dictionary, out);
   }
 
  private:
   ~LayerDebugInfo() override {}
   std::string name_;
 };
@@ skipping 284 matching lines @@
       children_.end(),
       std::bind2nd(std::mem_fun(&Layer::RemoveAnimatorsInTreeFromCollection),
                    collection));
 }
 
 bool Layer::IsAnimating() const {
   return animator_.get() && animator_->is_animating();
 }
 
 }  // namespace ui