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

gpu/tools/compositor_model_bench/shaders.h

 // Copyright (c) 2011 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.
 
 // Shaders from Chromium and an interface for setting them up
 
 #ifndef GPU_TOOLS_COMPOSITOR_MODEL_BENCH_SHADERS_H_
 #define GPU_TOOLS_COMPOSITOR_MODEL_BENCH_SHADERS_H_
 
 #include <string>
 
 // Forward declarations.
 class CCNode;
 class ContentLayerNode;
 
 typedef unsigned int GLuint;
 
 enum ShaderID {
   SHADER_UNRECOGNIZED = 0,
   VERTEX_SHADER_POS_TEX_YUV_STRETCH,
   VERTEX_SHADER_POS_TEX,
   VERTEX_SHADER_POS_TEX_TRANSFORM,
   FRAGMENT_SHADER_YUV_VIDEO,
   FRAGMENT_SHADER_RGBA_TEX_FLIP_ALPHA,
   FRAGMENT_SHADER_RGBA_TEX_ALPHA,
   SHADER_ID_MAX
 };
 
-ShaderID ShaderIDFromString(std::string name);
+ShaderID ShaderIDFromString(const std::string& name);
 std::string ShaderNameFromID(ShaderID id);
 
 void ConfigAndActivateShaderForNode(CCNode* n);
 
 // Call once to set up the parameters for an entire tiled layer, then use
 // DrawTileQuad for each tile to be drawn.
 void ConfigAndActivateShaderForTiling(ContentLayerNode* n);
 
 // One-off function to set up global VBO's that will be used every time
 // we want to draw a quad.
 void InitBuffers();
 
 // Per-frame initialization of the VBO's (to replicate behavior in Chrome.)
 void BeginFrame();
 
 // Draw the quad in those VBO's.
 void DrawQuad(float width, float height);
 
 // Draw the quad in those VBO's for an individual tile within a tiled layer.
 // x and y give the 2D index of the tile.
 void DrawTileQuad(GLuint texID, int x, int y);
 
 #endif  // GPU_TOOLS_COMPOSITOR_MODEL_BENCH_SHADERS_H_