WIP: diff which plumbs through the event URL.

chrome/test/data/extensions/webui/send_message.js

Index: chrome/test/data/extensions/webui/send_message.js
diff --git a/chrome/test/data/extensions/webui/send_message.js b/chrome/test/data/extensions/webui/send_message.js
index 69ab31429a92caa30db5c0c63c6526f111b528ef..2524e2c7e8602b9e65ab5595a0e7a929d91616aa 100644
--- a/chrome/test/data/extensions/webui/send_message.js
+++ b/chrome/test/data/extensions/webui/send_message.js
@@ -4,6 +4,13 @@
 
 // out/Debug/browser_tests --gtest_filter=ExtensionWebUITest.SendMessage
 
+if (!chrome || !chrome.test || !chrome.test.sendMessage) {
+  console.error('chrome.test.sendMessage is unavailable on ' +
+                document.location.href);
+  domAutomationController.send(false);
+  return;
+}
+
 chrome.test.sendMessage('ping', function(reply) {
   if (reply != 'pong') {
     console.error('Expected "pong", Actual ' + JSON.stringify(reply));