Make sure only platform app support <webview> tag

chrome/renderer/extensions/dispatcher.cc

Index: chrome/renderer/extensions/dispatcher.cc
diff --git a/chrome/renderer/extensions/dispatcher.cc b/chrome/renderer/extensions/dispatcher.cc
index 887a26df22a8931c14243bb13e37ebe5eeeae364..452796564bdeddc3e404e65954eff50042dad0ee 100644
--- a/chrome/renderer/extensions/dispatcher.cc
+++ b/chrome/renderer/extensions/dispatcher.cc
@@ -977,11 +977,16 @@ void Dispatcher::DidCreateScriptContext(
     }
   }
 
+  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)) {