Use FrameTreeNode ID as frameId in extension APIs

chrome/test/data/extensions/api_test/webnavigation/crossProcessIframe/frame.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.
+
+onload = function() {
+  setTimeout(function() {
+    if (location.hostname === 'a.com') {
+      // Notify the parent frame, so they can navigate us.
+      parent.postMessage('a.com: go to b.com', location.ancestorOrigins[0]);
+    } else if (location.hostname === 'b.com') {
+      // Trigger a navigation to a site in another process.
+      location.hostname = 'c.com';
+    } else {
+      console.assert(location.hostname === 'c.com');
+      // Done.
+    }
+  }, 0);
+};