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..618ce16567139b078d9ff1990ce825572ba3a12e 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_;
+  };
+
   // |source_map| is a weak pointer.
   explicit ModuleSystem(SourceMap* source_map);
   virtual ~ModuleSystem();