Allow requesting Automation tree by tabId

chrome/common/extensions/api/automation.idl

 // Copyright 2014 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.
 
 // The <code>chrome.automation</code> API allows developers to access the
 // automation (accessibility) tree for the browser. This is a tree
 // representation, analogous to the DOM tree, which represents the
 // <em>semantic</em> structure of a page, and can be used to programmatically
 // interact with a page.
 [nocompile] namespace automation {
@@ skipping 71 matching lines @@
     static void addEventListener(
         DOMString eventType, AutomationListener listener, bool capture);
     static void removeEventListener(
         DOMString eventType, AutomationListener listener, bool capture);
   };
 
   // Called when the <code>AutomationTree</code> for the page is available.
   callback RootCallback = void(AutomationTree tree);
 
   interface Functions {
-    // Get the automation tree for the current tab, enabling automation if
-    // necessary. Returns a tree with a placeholder root node; listen for
-    // the "load_complete" event to get a notification that the tree has fully
-    // loaded (the previous root node reference will stop working at or before
-    // this point).
-    [nocompile] static void getTree(RootCallback callback);
+    // Get the automation tree for the tab with the given tabId, or the current
+    // tab if no tabID is given, enabling automation if necessary. Returns a
+    // tree with a placeholder root node; listen for the "loadComplete" event to
+    // get a notification that the tree has fully loaded (the previous root node
+    // reference will stop working at or before this point).
+    [nocompile] static void getTree(optional long tabId, RootCallback callback);
 
     // Get the automation tree for the desktop.
     [nocompile] static void getDesktop(RootCallback callback);
   };
 };