Make sure only platform app support <webview> tag

chrome/renderer/extensions/dispatcher.cc

 // 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.
 
 #include "chrome/renderer/extensions/dispatcher.h"
 
 #include "base/callback.h"
 #include "base/command_line.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/string_piece.h"
@@ skipping 959 matching lines @@
       // regardless of |context_type|. ExtensionAPI knows how to return the
       // correct APIs, however, until it doesn't have a 2MB overhead we can't
       // load it in every process.
       RegisterSchemaGeneratedBindings(module_system.get(),
                                       context,
                                       v8_context);
       break;
     }
   }
 
+  bool is_within_platform_app = extension && extension->is_platform_app();

[Charlie Reis, 2013/03/20 01:52:25]

Wait, you're changing behavior here.  We're using different frames to determine
the extension in this approach vs. calling IsWithinPlatformApp. 
IsWithinPlatformApp looks at frame->top, while this extension comes from frame
itself.

I don't understand the context well enough to know if that's always safe.  Why
change it?  Is there a reason it's better?

   // Inject custom JS into the platform app context.
-  if (IsWithinPlatformApp(frame))
+  if (is_within_platform_app)
     module_system->Require("platformApp");
 
-  if (context_type == Feature::BLESSED_EXTENSION_CONTEXT) {
+  // Only platform apps support the <webview> tag, because the "webView" and
+  // "denyWebView" modules will affect the performance of DOM modifications
+  // (http://crbug.com/196453).
+  if (context_type == Feature::BLESSED_EXTENSION_CONTEXT &&
+      is_within_platform_app) {
     // Note: setting up the WebView class here, not the chrome.webview API.
     // The API will be automatically set up when first used.
     if (extension->HasAPIPermission(APIPermission::kWebView)) {
       module_system->Require("webView");
       if (Feature::GetCurrentChannel() <= chrome::VersionInfo::CHANNEL_DEV)
         module_system->Require("webViewExperimental");
     } else {
       module_system->Require("denyWebView");
     }
   }
@@ skipping 326 matching lines @@
     std::string error_msg = base::StringPrintf(kMessage, function_name.c_str());
     v8::ThrowException(
         v8::Exception::Error(v8::String::New(error_msg.c_str())));
     return false;
   }
 
   return true;
 }
 
 }  // namespace extensions