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_;
+    DISALLOW_COPY_AND_ASSIGN(NativesEnabledScope);
+  };
+
   // |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);
 
   // Register |native_handler| as a potential target for requireNative(), so
   // calls to requireNative(|name|) from JS will return a new object created by
   // |native_handler|.
   void RegisterNativeHandler(const std::string& name,
                              scoped_ptr<NativeHandler> native_handler);
 
   // Executes |code| in the current context with |name| as the filename.
   void RunString(const std::string& code, const std::string& name);
 
-  // When false |natives_enabled_| causes calls to GetNative() (the basis of
-  // requireNative() in JS) to throw an exception.
-  void set_natives_enabled(bool natives_enabled) {
-    natives_enabled_ = natives_enabled;
-  }
-
-  static v8::Handle<v8::Value> GetterRouter(v8::Local<v8::String> property,
-                                            const v8::AccessorInfo& info);
+  // Retrieves the lazily defined field specified by |property|.
+  static v8::Handle<v8::Value> LazyFieldGetter(v8::Local<v8::String> property,
+                                               const v8::AccessorInfo& info);
 
   // Make |object|.|field| lazily evaluate to the result of
   // require(|module_name|)[|module_field|].
   void SetLazyField(v8::Handle<v8::Object> object,
                     const std::string& field,
                     const std::string& module_name,
                     const std::string& module_field);
 
  private:
   typedef std::map<std::string, linked_ptr<NativeHandler> > NativeHandlerMap;
@@ skipping 18 matching lines @@
   // Wraps |source| in a (function(require, requireNative, exports) {...}).
   v8::Handle<v8::String> WrapSource(v8::Handle<v8::String> source);
 
   // Throws an exception in the calling JS context.
   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_;
+  // When 0, natives are disabled, otherwise indicates how many callers have
+  // pinned natives as enabled.
+  int natives_enabled_;
+
+  DISALLOW_COPY_AND_ASSIGN(ModuleSystem);
 };
 
 #endif  // CHROME_RENDERER_MODULE_SYSTEM_H_