Cleanup: Pass std::string as const reference from gpu/

gpu/tools/compositor_model_bench/render_tree.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 "gpu/tools/compositor_model_bench/render_tree.h"
 
 #include <sstream>
 #include <vector>
 
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/json/json_reader.h"
 #include "base/json/json_writer.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/values.h"
 
 #include "gpu/tools/compositor_model_bench/shaders.h"
 
 using base::JSONReader;
 using base::JSONWriter;
 using base::ReadFileToString;
 using std::string;
 using std::vector;
 
-GLenum TextureFormatFromString(std::string format) {
+GLenum TextureFormatFromString(const std::string& format) {
   if (format == "RGBA")
     return GL_RGBA;
   if (format == "RGB")
     return GL_RGB;
   if (format == "LUMINANCE")
     return GL_LUMINANCE;
   return GL_INVALID_ENUM;
 }
 
 const char* TextureFormatName(GLenum format) {
@@ skipping 435 matching lines @@
     base::DictionaryValue* v = static_cast<base::DictionaryValue*>(root.get());
     RenderNode* tree = InterpretContentLayer(v);
     return tree;
   } else {
     LOG(ERROR) << path.LossyDisplayName() <<
         " doesn not encode a JSON dictionary.";
     return NULL;
   }
 }