Reimplement automation API on top of C++-backed AXTree.

chrome/renderer/resources/extensions/automation_custom_bindings.js

 // 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.
 
 // Custom bindings for the automation API.
 var AutomationNode = require('automationNode').AutomationNode;
 var AutomationRootNode = require('automationNode').AutomationRootNode;
 var automation = require('binding').Binding.create('automation');
 var automationInternal =
     require('binding').Binding.create('automationInternal').generate();
 var eventBindings = require('event_bindings');
 var Event = eventBindings.Event;
 var forEach = require('utils').forEach;
 var lastError = require('lastError');
 var logging = requireNative('logging');
 var nativeAutomationInternal = requireNative('automationInternal');
 var GetRoutingID = nativeAutomationInternal.GetRoutingID;
 var GetSchemaAdditions = nativeAutomationInternal.GetSchemaAdditions;
+var DestroyAccessibilityTree =
+    nativeAutomationInternal.DestroyAccessibilityTree;
+var GetIntAttribute = nativeAutomationInternal.GetIntAttribute;
+var StartCachingAccessibilityTrees =
+    nativeAutomationInternal.StartCachingAccessibilityTrees;
 var schema = GetSchemaAdditions();
 
 /**
  * A namespace to export utility functions to other files in automation.
  */
 window.automationUtil = function() {};
 
 // TODO(aboxhall): Look into using WeakMap
-var idToAutomationRootNode = {};
 var idToCallback = {};
 
 var DESKTOP_TREE_ID = 0;
 
 automationUtil.storeTreeCallback = function(id, callback) {
   if (!callback)
     return;
 
-  var targetTree = idToAutomationRootNode[id];
+  var targetTree = AutomationRootNode.get(id);
   if (!targetTree) {
     // If we haven't cached the tree, hold the callback until the tree is
     // populated by the initial onAccessibilityEvent call.
     if (id in idToCallback)
       idToCallback[id].push(callback);
     else
       idToCallback[id] = [callback];
   } else {
     callback(targetTree);
   }
 };
 
 /**
  * Global list of tree change observers.
  * @type {Array<TreeChangeObserver>}
  */
 automationUtil.treeChangeObservers = [];
 
 automation.registerCustomHook(function(bindingsAPI) {
   var apiFunctions = bindingsAPI.apiFunctions;
 
   // TODO(aboxhall, dtseng): Make this return the speced AutomationRootNode obj.
   apiFunctions.setHandleRequest('getTree', function getTree(tabID, callback) {
     var routingID = GetRoutingID();
+    StartCachingAccessibilityTrees();
 
     // enableTab() ensures the renderer for the active or specified tab has
     // accessibility enabled, and fetches its ax tree id to use as
     // a key in the idToAutomationRootNode map. The callback to
     // enableTab is bound to the callback passed in to getTree(), so that once
     // the tree is available (either due to having been cached earlier, or after
     // an accessibility event occurs which causes the tree to be populated), the
     // callback can be called.
     var params = { routingID: routingID, tabID: tabID };
     automationInternal.enableTab(params,
         function onEnable(id) {
           if (lastError.hasError(chrome)) {
             callback();
             return;
           }
           automationUtil.storeTreeCallback(id, callback);
         });
   });
 
   var desktopTree = null;
   apiFunctions.setHandleRequest('getDesktop', function(callback) {
-    desktopTree =
-        idToAutomationRootNode[DESKTOP_TREE_ID];
+    StartCachingAccessibilityTrees();
+    desktopTree = AutomationRootNode.get(DESKTOP_TREE_ID);
     if (!desktopTree) {
       if (DESKTOP_TREE_ID in idToCallback)
         idToCallback[DESKTOP_TREE_ID].push(callback);
       else
         idToCallback[DESKTOP_TREE_ID] = [callback];
 
       var routingID = GetRoutingID();
 
       // TODO(dtseng): Disable desktop tree once desktop object goes out of
       // scope.
       automationInternal.enableDesktop(routingID, function() {
         if (lastError.hasError(chrome)) {
-          delete idToAutomationRootNode[
-              DESKTOP_TREE_ID];
+          AutomationRootNode.destroy(DESKTOP_TREE_ID);
           callback();
           return;
         }
       });
     } else {
       callback(desktopTree);
     }
   });
 
   function removeTreeChangeObserver(observer) {
@@ skipping 10 matching lines @@
   function addTreeChangeObserver(observer) {
     removeTreeChangeObserver(observer);
     automationUtil.treeChangeObservers.push(observer);
   }
   apiFunctions.setHandleRequest('addTreeChangeObserver', function(observer) {
     addTreeChangeObserver(observer);
   });
 
 });
 
+automationInternal.onTreeChange.addListener(function(treeID,
+                                                     nodeID,
+                                                     changeType) {
+  var tree = AutomationRootNode.get(treeID);
+  if (!tree)
+    return;
+
+  var node = privates(tree).impl.get(nodeID);
+  if (!node)
+    return;
+
+  if (node.role == 'webView') {
+    var childTreeID = GetIntAttribute(treeID, nodeID, 'childTreeId');

[aboxhall, 2015/06/11 17:42:46]

Can you add a comment explaining what's going on in this block?

[dmazzoni, 2015/06/12 17:51:36]

Done. This code used to be in automation_node.js.

+    if (!AutomationRootNode.get(childTreeID)) {
+      automationUtil.storeTreeCallback(childTreeID, function(root) {
+        privates(root).impl.hostNode = node;
+
+        if (root.docLoaded)
+          privates(root).impl.dispatchEvent(schema.EventType.loadComplete);
+
+        privates(node).impl.dispatchEvent(schema.EventType.childrenChanged);
+      });
+
+      automationInternal.enableFrame(childTreeID);
+    }
+  }
+
+  var treeChange = {target: node, type: changeType};
+  var observers = automationUtil.treeChangeObservers;
+  for (var i = 0; i < observers.length; i++) {
+    try {
+      observers[i](treeChange);
+    } catch (e) {
+      console.error('Error in tree change observer for ' +

[aboxhall, 2015/06/11 17:42:46]

Maybe use logging.WARNING - logs to stderr.
https://code.google.com/p/chromium/codesearch#chromium/src/extensions/rendere...

Extension developers will be able to see console.logs (though that may be what
we want here?)

[dmazzoni, 2015/06/12 17:51:36]

This is intended for extension developers. Which is better?

+          treeChange.type + ': ' + e.message +
+          '\nStack trace: ' + e.stack);
+    }
+  }
+
+  //
+  // TODO: delete AutomationNode if 'removeNode' event
+  //
+});
+
 // Listen to the automationInternal.onAccessibilityEvent event, which is
 // essentially a proxy for the AccessibilityHostMsg_Events IPC from the
 // renderer.
 automationInternal.onAccessibilityEvent.addListener(function(data) {
   var id = data.treeID;
-  var targetTree = idToAutomationRootNode[id];
-  if (!targetTree) {
-    // If this is the first time we've gotten data for this tree, it will
-    // contain all of the tree's data, so create a new tree which will be
-    // bootstrapped from |data|.
-    targetTree = new AutomationRootNode(id);
-    idToAutomationRootNode[id] = targetTree;
-  }
+  var targetTree = AutomationRootNode.getOrCreate(id);
+
   if (!privates(targetTree).impl.onAccessibilityEvent(data))
     return;
 
   // If we're not waiting on a callback to getTree(), we can early out here.
   if (!(id in idToCallback))
     return;
 
   // We usually get a 'placeholder' tree first, which doesn't have any url
   // attribute or child nodes. If we've got that, wait for the full tree before
   // calling the callback.
   // TODO(dmazzoni): Don't send down placeholder (crbug.com/397553)
-  if (id != DESKTOP_TREE_ID && !targetTree.attributes.url &&
+  if (id != DESKTOP_TREE_ID && !targetTree.url &&
       targetTree.children.length == 0) {
     return;
   }
 
   // If the tree wasn't available when getTree() was called, the callback will
   // have been cached in idToCallback, so call and delete it now that we
   // have the complete tree.
   for (var i = 0; i < idToCallback[id].length; i++) {
-    console.log('calling getTree() callback');
     var callback = idToCallback[id][i];
     callback(targetTree);
   }
   delete idToCallback[id];
 });
 
 automationInternal.onAccessibilityTreeDestroyed.addListener(function(id) {
-  var targetTree = idToAutomationRootNode[id];
+  // Destroy the native cache of the accessibility tree.
+  DestroyAccessibilityTree(id);
+
+  // Destroy the AutomationRootNode.
+  var targetTree = AutomationRootNode.get(id);
   if (targetTree) {
     privates(targetTree).impl.destroy();
-    delete idToAutomationRootNode[id];
+    AutomationRootNode.destroy(id);
   } else {
     logging.WARNING('no targetTree to destroy');
   }
-  delete idToAutomationRootNode[id];
 });
 
 exports.binding = automation.generate();
 
 // Add additional accessibility bindings not specified in the automation IDL.
 // Accessibility and automation share some APIs (see
 // ui/accessibility/ax_enums.idl).
 forEach(schema, function(k, v) {
   exports.binding[k] = v;
 });