Fix message routing for BrowserPlugin in iframe

chrome/test/data/extensions/platform_apps/web_view/inside_iframe/main.js

Index: chrome/test/data/extensions/platform_apps/web_view/inside_iframe/main.js
diff --git a/chrome/test/data/extensions/platform_apps/web_view/rules_registry/main.js b/chrome/test/data/extensions/platform_apps/web_view/inside_iframe/main.js
similarity index 62%
copy from chrome/test/data/extensions/platform_apps/web_view/rules_registry/main.js
copy to chrome/test/data/extensions/platform_apps/web_view/inside_iframe/main.js
index 85de24737bdb12608aba361741daf5bc8ae6e9cb..a8e61c170ee3a6a251700011db62244211fd3e84 100644
--- a/chrome/test/data/extensions/platform_apps/web_view/rules_registry/main.js
+++ b/chrome/test/data/extensions/platform_apps/web_view/inside_iframe/main.js
@@ -3,12 +3,17 @@
 // found in the LICENSE file.
 
 var startTest = function() {
-  document.querySelector('#webview-tag-container').innerHTML =
+  var iframeWindow = document.querySelector('iframe').contentWindow;
+  iframeWindow.document.querySelector('#webview-tag-container').innerHTML =
       '<webview style="width: 10px; height: 10px; margin: 0; padding: 0;"' +
       '></webview>';
 
-  var webview = document.querySelector('webview');
+  var webview = iframeWindow.document.querySelector('webview');
   var onLoadStop = function(e) {
+    if (!webview.contentWindow) {
+      chrome.test.sendMessage('WebViewTest.FAILURE');
+      return;
+    }
     chrome.test.sendMessage('WebViewTest.LAUNCHED');
   };