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

chrome/renderer/module_system.h

Index: chrome/renderer/module_system.h
diff --git a/chrome/renderer/module_system.h b/chrome/renderer/module_system.h
index 4a50938650894c068e835bf915288ef6c0127b15..8b88d7c5e57625d2b2c82968eb42582743c55226 100644
--- a/chrome/renderer/module_system.h
+++ b/chrome/renderer/module_system.h
@@ -39,6 +39,16 @@ class ModuleSystem : public NativeHandler {
     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_;

[not at google - send to devlin, 2012/03/26 02:29:49]

Come to think of it this is still subtly flawed, since copying or assigning one
of these won't increment the counter, but destruction will still decrement it.
So maybe you should DISALLOW_COPY_AND_ASSIGN (and come to think of it so should
ModuleSystem).

Or... you could do something totally sweet and make those increment the counter,
and then have ModuleSystem construct and return its own NativesEnabledScopes!

Just kidding. Kinda.

[koz (OOO until 15th September), 2012/03/26 03:58:59]

lol, maybe I'll just add the DISALLOW_COPY_AND_ASSIGN for now...

+  };
+
   // |source_map| is a weak pointer.
   explicit ModuleSystem(SourceMap* source_map);
   virtual ~ModuleSystem();
@@ -59,14 +69,9 @@ class ModuleSystem : public NativeHandler {
   // 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|].
@@ -105,7 +110,9 @@ class ModuleSystem : public NativeHandler {
   // 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_;
 };
 
 #endif  // CHROME_RENDERER_MODULE_SYSTEM_H_