Make app_custom_bindings.js lazily evaluated so it doesn't execute on every page load.

chrome/renderer/module_system.h

 // 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.
 
 #ifndef CHROME_RENDERER_MODULE_SYSTEM_H_
 #define CHROME_RENDERER_MODULE_SYSTEM_H_
 #pragma once
 
 #include "base/compiler_specific.h"
 #include "base/memory/linked_ptr.h"
@@ skipping 21 matching lines @@
 // v8::Context.
 // TODO(koz): Rename this to JavaScriptModuleSystem.
 class ModuleSystem : public NativeHandler {
  public:
   class SourceMap {
    public:
     virtual v8::Handle<v8::Value> GetSource(const std::string& name) = 0;
     virtual bool Contains(const std::string& name) = 0;
   };
 
+  // Enables native bindings for the duration of its lifetime.
+  class NativesEnabledScope {
+   public:
+    explicit NativesEnabledScope(ModuleSystem* module_system);
+    ~NativesEnabledScope();
+
+   private:
+    ModuleSystem* module_system_;
+  };
+
   // |source_map| is a weak pointer.
   explicit ModuleSystem(SourceMap* source_map);
   virtual ~ModuleSystem();
 
   // Require the specified module. This is the equivalent of calling
   // require('module_name') from the loaded JS files.
   void Require(const std::string& module_name);
   v8::Handle<v8::Value> Require(const v8::Arguments& args);
   v8::Handle<v8::Value> RequireForJs(const v8::Arguments& args);
   v8::Handle<v8::Value> RequireForJsInner(v8::Handle<v8::String> module_name);
@@ skipping 50 matching lines @@
   v8::Handle<v8::Value> ThrowException(const std::string& message);
 
   // A map from module names to the JS source for that module. GetSource()
   // performs a lookup on this map.
   SourceMap* source_map_;
   NativeHandlerMap native_handler_map_;
   bool natives_enabled_;
 };
 
 #endif  // CHROME_RENDERER_MODULE_SYSTEM_H_