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

chrome/renderer/resources/extensions/automation_custom_bindings.js

Index: chrome/renderer/resources/extensions/automation_custom_bindings.js
diff --git a/chrome/renderer/resources/extensions/automation_custom_bindings.js b/chrome/renderer/resources/extensions/automation_custom_bindings.js
index b2fc5c3b711d1b9dc49fb8c04648d91c33aef577..3f8e44680023a4d4a26841e19cc507db21cbec79 100644
--- a/chrome/renderer/resources/extensions/automation_custom_bindings.js
+++ b/chrome/renderer/resources/extensions/automation_custom_bindings.js
@@ -16,6 +16,11 @@ 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();
 
 /**
@@ -24,7 +29,6 @@ var schema = GetSchemaAdditions();
 window.automationUtil = function() {};
 
 // TODO(aboxhall): Look into using WeakMap
-var idToAutomationRootNode = {};
 var idToCallback = {};
 
 var DESKTOP_TREE_ID = 0;
@@ -33,7 +37,7 @@ 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.
@@ -58,6 +62,7 @@ automation.registerCustomHook(function(bindingsAPI) {
   // 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
@@ -79,8 +84,8 @@ automation.registerCustomHook(function(bindingsAPI) {
 
   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);
@@ -93,8 +98,7 @@ automation.registerCustomHook(function(bindingsAPI) {
       // scope.
       automationInternal.enableDesktop(routingID, function() {
         if (lastError.hasError(chrome)) {
-          delete idToAutomationRootNode[
-              DESKTOP_TREE_ID];
+          AutomationRootNode.destroy(DESKTOP_TREE_ID);
           callback();
           return;
         }
@@ -125,19 +129,62 @@ automation.registerCustomHook(function(bindingsAPI) {
 
 });
 
+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') {
+    // A WebView in the desktop tree has a different AX tree as its child.
+    // When we encounter a WebView with a child AX tree id that we don't
+    // currently have cached, explicitly request that AX tree from the
+    // browser process and set up a callback when it loads to attach that
+    // tree as a child of this node and fire appropriate events.
+    var childTreeID = GetIntAttribute(treeID, nodeID, 'childTreeId');
+    if (!AutomationRootNode.get(childTreeID)) {
+      automationUtil.storeTreeCallback(childTreeID, function(root) {
+        privates(root).impl.hostNode = node;

[not at google - send to devlin, 2015/06/17 21:14:48]

Glancing at this code (and not understanding it), the frequency of
"privates(root).impl" makes me think whatever this is doing should be pulled
into the class itself. Like,
privates(root).impl.setHostNodeForSomethingSomething(node).

[dmazzoni, 2015/06/18 07:23:53]

Done.

[not at google - send to devlin, 2015/06/18 17:34:38]

Is there a semantically reasonable function that could fire those
privates(root).impl.dispatchEvent() functions as well?

[dmazzoni, 2015/06/18 21:31:53]

I'm not sure why - I consider automation_custom_bindings.js and
automation_node.js to be almost friend classes - they're both implementing
private impl classes that the client doesn't see, I don't see any reason to add
layers of abstraction around calling a function on AutomationNodeImpl vs one on
AutomationNode. Or am I misunderstanding your concern?

+
+        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;

[not at google - send to devlin, 2015/06/17 21:14:48]

I don't know where this code came from, but note that extension events have had
problems with listeners adding or removing other listeners from within their
callbacks, which this code isn't safe against.

[dmazzoni, 2015/06/18 07:23:53]

Good idea. I changed it to make a copy of the array first.

+  for (var i = 0; i < observers.length; i++) {
+    try {
+      observers[i](treeChange);
+    } catch (e) {
+      logging.WARNING('Error in tree change observer for ' +
+          treeChange.type + ': ' + e.message +
+          '\nStack trace: ' + e.stack);
+    }
+  }
+
+  if (changeType == schema.TreeChangeType.nodeRemoved) {
+    privates(tree).impl.remove(nodeID);
+  }
+});
+
 // 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;
 
@@ -149,7 +196,7 @@ automationInternal.onAccessibilityEvent.addListener(function(data) {
   // 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;
   }
@@ -158,7 +205,6 @@ automationInternal.onAccessibilityEvent.addListener(function(data) {
   // 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);
   }
@@ -166,14 +212,17 @@ automationInternal.onAccessibilityEvent.addListener(function(data) {
 });
 
 automationInternal.onAccessibilityTreeDestroyed.addListener(function(id) {
-  var targetTree = idToAutomationRootNode[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];
+
+  // Destroy the native cache of the accessibility tree.
+  DestroyAccessibilityTree(id);
 });
 
 exports.binding = automation.generate();