Don't send unnecessary ExtensionMsg_Loaded IPCs.

chrome/test/data/extensions/api_test/permissions/optional_updates_bindings/background.js

+// Copyright 2015 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.
+
+// window.html will turn around and call this when it loads.
+// |otherWindow| is its window object.
+function runTest(otherWindow) {
+  chrome.test.runWithUserGesture(function() {
+    chrome.permissions.request({permissions: ['alarms']}, function(granted) {
+      chrome.test.assertTrue(granted);
+      // Assert that the bindings have been updated on ourselves the background
+      // page, and the tab that was created.
+      var expectedAlarmsKeys = [
+          'clear', 'clearAll', 'create', 'get', 'getAll', 'onAlarm'];
+      [window, otherWindow].forEach(function(w) {
+        chrome.test.assertEq(expectedAlarmsKeys,
+                             Object.keys(w.chrome.alarms).sort());

[Devlin, 2015/06/03 20:53:37]

While the alarms api is pretty stable, I think it'd still be the right-er thing
to do to make sure that we contain at least those keys, versus strict equality.

[not at google - send to devlin, 2015/06/03 21:53:03]

I think it's stronger to check all, and I don't see why not. I picked alarms
specifically because it's almost certainly not going to change, but if somebody
does decide to add something for some reason, we can update it then.

+      });
+      chrome.test.succeed();
+    });
+  });
+}
+
+// This is the important part; creating a new window would cause the optional
+// pemissions to be updated on itself, rather than both the window and the
+// background page.
+chrome.tabs.create({url: 'window.html'});