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

chrome/renderer/extensions/automation_internal_custom_bindings.cc

 // 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.
 
 #include "chrome/renderer/extensions/automation_internal_custom_bindings.h"
 
 #include "base/bind.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/values.h"
 #include "chrome/common/extensions/chrome_extension_messages.h"
@@ skipping 21 matching lines @@
         isolate, ui::ToString(static_cast<EnumType>(i)).c_str());
     object->Set(value, value);
   }
   return object;
 }
 
 }  // namespace
 
 namespace extensions {
 
+TreeCache::TreeCache() {}
+TreeCache::~TreeCache() {}
+
 class AutomationMessageFilter : public IPC::MessageFilter {
  public:
   explicit AutomationMessageFilter(AutomationInternalCustomBindings* owner)
       : owner_(owner),
         removed_(false) {
     DCHECK(owner);
     content::RenderThread::Get()->AddFilter(this);
+    task_runner_ = content::RenderThread::Get()->GetTaskRunner();
   }
 
   void Detach() {
     owner_ = nullptr;
     Remove();
   }
 
   // IPC::MessageFilter
   bool OnMessageReceived(const IPC::Message& message) override {
-    if (owner_)
-      return owner_->OnMessageReceived(message);
-    else
-      return false;
+    task_runner_->PostTask(
+        FROM_HERE,
+        base::Bind(
+            &AutomationMessageFilter::OnMessageReceivedOnRenderThread,
+            this, message));
+    return false;
   }
 
   void OnFilterRemoved() override {
     removed_ = true;
   }
 
 private:
+  void OnMessageReceivedOnRenderThread(const IPC::Message& message) {
+    if (owner_)
+      owner_->OnMessageReceived(message);
+  }
+
   ~AutomationMessageFilter() override {
     Remove();
   }
 
   void Remove() {
     if (!removed_) {
       removed_ = true;
       content::RenderThread::Get()->RemoveFilter(this);
     }
   }
 
   AutomationInternalCustomBindings* owner_;
   bool removed_;
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
 
   DISALLOW_COPY_AND_ASSIGN(AutomationMessageFilter);
 };
 
 AutomationInternalCustomBindings::AutomationInternalCustomBindings(
     ScriptContext* context) : ObjectBackedNativeHandler(context) {
   // It's safe to use base::Unretained(this) here because these bindings
   // will only be called on a valid AutomationInternalCustomBindings instance
   // and none of the functions have any side effects.
-  RouteFunction(
-      "IsInteractPermitted",
-      base::Bind(&AutomationInternalCustomBindings::IsInteractPermitted,
-                 base::Unretained(this)));
-  RouteFunction(
-      "GetSchemaAdditions",
-      base::Bind(&AutomationInternalCustomBindings::GetSchemaAdditions,
-                 base::Unretained(this)));
-  RouteFunction(
-      "GetRoutingID",
-      base::Bind(&AutomationInternalCustomBindings::GetRoutingID,
-                 base::Unretained(this)));
+  #define ROUTE_FUNCTION(FN) \
+  RouteFunction(#FN, \
+                base::Bind(&AutomationInternalCustomBindings::FN, \
+                base::Unretained(this)))
 
-  message_filter_ = new AutomationMessageFilter(this);
+  ROUTE_FUNCTION(IsInteractPermitted);
+  ROUTE_FUNCTION(GetSchemaAdditions);
+  ROUTE_FUNCTION(GetRoutingID);
+  ROUTE_FUNCTION(StartCachingAccessibilityTrees);
+  ROUTE_FUNCTION(DestroyAccessibilityTree);
+  ROUTE_FUNCTION(GetRootID);
+  ROUTE_FUNCTION(GetParentID);
+  ROUTE_FUNCTION(GetChildCount);
+  ROUTE_FUNCTION(GetChildIDAtIndex);
+  ROUTE_FUNCTION(GetIndexInParent);
+  ROUTE_FUNCTION(GetState);
+  ROUTE_FUNCTION(GetRole);
+  ROUTE_FUNCTION(GetLocation);
+  ROUTE_FUNCTION(GetStringAttribute);
+  ROUTE_FUNCTION(GetBoolAttribute);
+  ROUTE_FUNCTION(GetIntAttribute);
+  ROUTE_FUNCTION(GetFloatAttribute);
+  ROUTE_FUNCTION(GetIntListAttribute);
+  ROUTE_FUNCTION(GetHtmlAttribute);
+
+  #undef ROUTE_FUNCTION
 }
 
 AutomationInternalCustomBindings::~AutomationInternalCustomBindings() {
-  message_filter_->Detach();
+  if (message_filter_)
+    message_filter_->Detach();
+  STLDeleteContainerPairSecondPointers(tree_id_to_tree_cache_map_.begin(),
+                                       tree_id_to_tree_cache_map_.end());
 }
 
 bool AutomationInternalCustomBindings::OnMessageReceived(
     const IPC::Message& message) {

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

1. There doesn't seem much point this method imitating the OnMessageReceived
interface anymore, specifically, the way it returns a bool. The comment should
be moved up to the "return false" on AutomationMessageFilter::OnMessageReceived.

2. Given the above point, isn't there some way of saying that some message must
be handled on some thread, and then returning a bool makes sense again?

3. There should probably be a guard against is_valid() in here. There should
always have been, in fact. I wonder where else we have this problem.

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

Good call, done.
I don't think it makes sense for it to be an error if nobody handles the
message. It's not hard to imagine a scenario where this
AutomationInternalCustomBindings object gets deleted but there are still IPCs in
flight destined for this process.
Sorry, I don't understand - I don't see is_valid() checks in most message
handlers, can you point me to an example?

   IPC_BEGIN_MESSAGE_MAP(AutomationInternalCustomBindings, message)
     IPC_MESSAGE_HANDLER(ExtensionMsg_AccessibilityEvent, OnAccessibilityEvent)
   IPC_END_MESSAGE_MAP()
 
   // Always return false in case there are multiple
   // AutomationInternalCustomBindings instances attached to the same thread.
   return false;
 }
 
 void AutomationInternalCustomBindings::IsInteractPermitted(
     const v8::FunctionCallbackInfo<v8::Value>& args) {
   const Extension* extension = context()->extension();
   CHECK(extension);
   const AutomationInfo* automation_info = AutomationInfo::Get(extension);
   CHECK(automation_info);
   args.GetReturnValue().Set(
       v8::Boolean::New(GetIsolate(), automation_info->interact));
 }
 
 void AutomationInternalCustomBindings::GetRoutingID(
     const v8::FunctionCallbackInfo<v8::Value>& args) {
   int routing_id = context()->GetRenderView()->GetRoutingID();
   args.GetReturnValue().Set(v8::Integer::New(GetIsolate(), routing_id));
 }
 
+void AutomationInternalCustomBindings::StartCachingAccessibilityTrees(
+    const v8::FunctionCallbackInfo<v8::Value>& args) {
+  if (!message_filter_)
+    message_filter_ = new AutomationMessageFilter(this);
+}
+
 void AutomationInternalCustomBindings::GetSchemaAdditions(
     const v8::FunctionCallbackInfo<v8::Value>& args) {
   v8::Local<v8::Object> additions = v8::Object::New(GetIsolate());
 
   additions->Set(
       v8::String::NewFromUtf8(GetIsolate(), "EventType"),
       ToEnumObject(GetIsolate(), ui::AX_EVENT_NONE, ui::AX_EVENT_LAST));
 
   additions->Set(
       v8::String::NewFromUtf8(GetIsolate(), "RoleType"),
       ToEnumObject(GetIsolate(), ui::AX_ROLE_NONE, ui::AX_ROLE_LAST));
 
   additions->Set(
       v8::String::NewFromUtf8(GetIsolate(), "StateType"),
       ToEnumObject(GetIsolate(), ui::AX_STATE_NONE, ui::AX_STATE_LAST));
 
   additions->Set(
       v8::String::NewFromUtf8(GetIsolate(), "TreeChangeType"),
       ToEnumObject(GetIsolate(), ui::AX_MUTATION_NONE, ui::AX_MUTATION_LAST));
 
   args.GetReturnValue().Set(additions);
 }
 
+void AutomationInternalCustomBindings::DestroyAccessibilityTree(
+    const v8::FunctionCallbackInfo<v8::Value>& args) {
+  if (args.Length() != 1 || !args[0]->IsNumber()) {
+    ThrowInvalidArgumentsException(args);
+    return;
+  }
+
+  int tree_id = args[0]->Int32Value();
+  auto iter = tree_id_to_tree_cache_map_.find(tree_id);
+  if (iter == tree_id_to_tree_cache_map_.end())
+    return;
+
+  TreeCache* cache = iter->second;
+  tree_id_to_tree_cache_map_.erase(tree_id);
+  axtree_to_tree_cache_map_.erase(&cache->tree);
+  delete cache;
+}
+
+//
+// Access the cached accessibility trees and properties of their nodes.
+//
+
+void AutomationInternalCustomBindings::GetRootID(
+    const v8::FunctionCallbackInfo<v8::Value>& args) {
+  if (args.Length() != 1 || !args[0]->IsNumber()) {
+    ThrowInvalidArgumentsException(args);
+    return;
+  }
+
+  int tree_id = args[0]->Int32Value();
+  const auto& iter = tree_id_to_tree_cache_map_.find(tree_id);

[not at google - send to devlin, 2015/06/17 21:14:47]

I think this shouldn't be a const reference, just a copy of the iterator. Same
elsewhere.

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

Done.

+  if (iter == tree_id_to_tree_cache_map_.end())
+    return;
+
+  TreeCache* cache = iter->second;
+  int root_id = cache->tree.root()->id();
+  args.GetReturnValue().Set(v8::Integer::New(GetIsolate(), root_id));
+}
+
+void AutomationInternalCustomBindings::GetParentID(
+    const v8::FunctionCallbackInfo<v8::Value>& args) {
+  ui::AXNode* node;

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

Always nice to initialise pointers to null.

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

Done.

+  if (!GetNodeHelper(args, nullptr, &node))
+    return;
+
+  if (!node->parent())
+    return;
+
+  int parent_id = node->parent()->id();
+  args.GetReturnValue().Set(v8::Integer::New(GetIsolate(), parent_id));
+}
+
+void AutomationInternalCustomBindings::GetChildCount(
+    const v8::FunctionCallbackInfo<v8::Value>& args) {
+  ui::AXNode* node;
+  if (!GetNodeHelper(args, nullptr, &node))
+    return;
+
+  int child_count = node->child_count();
+  args.GetReturnValue().Set(v8::Integer::New(GetIsolate(), child_count));
+}
+
+void AutomationInternalCustomBindings::GetChildIDAtIndex(
+    const v8::FunctionCallbackInfo<v8::Value>& args) {
+  if (args.Length() < 3 || !args[2]->IsNumber()) {
+    ThrowInvalidArgumentsException(args);
+    return;
+  }
+
+  ui::AXNode* node;
+  if (!GetNodeHelper(args, nullptr, &node))
+    return;
+
+  int index = args[2]->Int32Value();
+  if (index < 0 || index >= node->child_count())
+    return;
+
+  int child_id = node->children()[index]->id();
+  args.GetReturnValue().Set(v8::Integer::New(GetIsolate(), child_id));
+}
+
+void AutomationInternalCustomBindings::GetIndexInParent(
+    const v8::FunctionCallbackInfo<v8::Value>& args) {
+  ui::AXNode* node;
+  if (!GetNodeHelper(args, nullptr, &node))
+    return;
+
+  int index_in_parent = node->index_in_parent();
+  args.GetReturnValue().Set(v8::Integer::New(GetIsolate(), index_in_parent));
+}
+
+void AutomationInternalCustomBindings::GetState(
+    const v8::FunctionCallbackInfo<v8::Value>& args) {
+  ui::AXNode* node;
+  if (!GetNodeHelper(args, nullptr, &node))
+    return;
+
+  base::DictionaryValue state_dict;
+  uint32 state_pos = 0, state_shifter = node->data().state;
+  while (state_shifter) {
+    if (state_shifter & 1) {
+      state_dict.SetBoolean(
+          ToString(static_cast<ui::AXState>(state_pos)), true);
+    }
+    state_shifter = state_shifter >> 1;
+    state_pos++;
+  }
+
+  SetReturnValueFromBaseValue(args, state_dict);
+}
+
+void AutomationInternalCustomBindings::GetRole(
+    const v8::FunctionCallbackInfo<v8::Value>& args) {
+  ui::AXNode* node;
+  if (!GetNodeHelper(args, nullptr, &node))
+    return;
+
+  std::string role_name = ui::ToString(node->data().role);
+  args.GetReturnValue().Set(
+      v8::String::NewFromUtf8(GetIsolate(), role_name.c_str()));
+}
+
+void AutomationInternalCustomBindings::GetLocation(
+    const v8::FunctionCallbackInfo<v8::Value>& args) {
+  TreeCache* cache;
+  ui::AXNode* node;
+  if (!GetNodeHelper(args, &cache, &node))
+    return;
+
+  base::DictionaryValue location_dict;
+  gfx::Rect location = node->data().location;
+  location.Offset(cache->location_offset);
+  location_dict.SetInteger("left", location.x());
+  location_dict.SetInteger("top", location.y());
+  location_dict.SetInteger("width", location.width());
+  location_dict.SetInteger("height", location.height());
+
+  SetReturnValueFromBaseValue(args, location_dict);
+}
+
+void AutomationInternalCustomBindings::GetStringAttribute(
+    const v8::FunctionCallbackInfo<v8::Value>& args) {
+  ui::AXNode* node;
+  std::string attribute_name;
+  if (!GetAttributeHelper(args, &node, &attribute_name))
+    return;
+
+  ui::AXStringAttribute attribute = ui::ParseAXStringAttribute(attribute_name);
+  std::string attr_value;
+  if (!node->data().GetStringAttribute(attribute, &attr_value))
+    return;
+
+  args.GetReturnValue().Set(
+      v8::String::NewFromUtf8(GetIsolate(), attr_value.c_str()));
+}
+
+void AutomationInternalCustomBindings::GetBoolAttribute(
+    const v8::FunctionCallbackInfo<v8::Value>& args) {
+  ui::AXNode* node;
+  std::string attribute_name;
+  if (!GetAttributeHelper(args, &node, &attribute_name))
+    return;
+
+  ui::AXBoolAttribute attribute = ui::ParseAXBoolAttribute(attribute_name);
+  bool attr_value;
+  if (!node->data().GetBoolAttribute(attribute, &attr_value))
+    return;
+
+  args.GetReturnValue().Set(v8::Boolean::New(GetIsolate(), attr_value));
+}
+
+void AutomationInternalCustomBindings::GetIntAttribute(
+    const v8::FunctionCallbackInfo<v8::Value>& args) {
+  ui::AXNode* node;
+  std::string attribute_name;
+  if (!GetAttributeHelper(args, &node, &attribute_name))
+    return;
+
+  ui::AXIntAttribute attribute = ui::ParseAXIntAttribute(attribute_name);
+  int attr_value;
+  if (!node->data().GetIntAttribute(attribute, &attr_value))
+    return;
+
+  args.GetReturnValue().Set(v8::Integer::New(GetIsolate(), attr_value));
+}
+
+void AutomationInternalCustomBindings::GetFloatAttribute(
+    const v8::FunctionCallbackInfo<v8::Value>& args) {
+  ui::AXNode* node;
+  std::string attribute_name;
+  if (!GetAttributeHelper(args, &node, &attribute_name))
+    return;
+
+  ui::AXFloatAttribute attribute = ui::ParseAXFloatAttribute(attribute_name);
+  float attr_value;
+
+  if (!node->data().GetFloatAttribute(attribute, &attr_value))
+    return;
+
+  args.GetReturnValue().Set(v8::Number::New(GetIsolate(), attr_value));
+}
+
+void AutomationInternalCustomBindings::GetIntListAttribute(
+    const v8::FunctionCallbackInfo<v8::Value>& args) {
+  ui::AXNode* node;
+  std::string attribute_name;
+  if (!GetAttributeHelper(args, &node, &attribute_name))
+    return;
+
+  ui::AXIntListAttribute attribute =
+      ui::ParseAXIntListAttribute(attribute_name);
+  if (!node->data().HasIntListAttribute(attribute))
+    return;
+  const std::vector<int32>& attr_value =
+      node->data().GetIntListAttribute(attribute);
+
+  base::ListValue list;
+  for (int32 i : attr_value)
+    list.AppendInteger(i);
+  SetReturnValueFromBaseValue(args, list);
+}
+
+void AutomationInternalCustomBindings::GetHtmlAttribute(
+    const v8::FunctionCallbackInfo<v8::Value>& args) {
+  ui::AXNode* node;
+  std::string attribute_name;
+  if (!GetAttributeHelper(args, &node, &attribute_name))
+    return;
+
+  std::string attr_value;
+  if (!node->data().GetHtmlAttribute(attribute_name.c_str(), &attr_value))
+    return;
+
+  args.GetReturnValue().Set(
+      v8::String::NewFromUtf8(GetIsolate(), attr_value.c_str()));
+}
+
+//
+// Helper functions.
+//
+
+void AutomationInternalCustomBindings::ThrowInvalidArgumentsException(
+    const v8::FunctionCallbackInfo<v8::Value>& args) {
+  GetIsolate()->ThrowException(
+      v8::String::NewFromUtf8(
+          GetIsolate(),
+          "Invalid arguments to AutomationInternalCustomBindings function",
+          v8::NewStringType::kNormal).ToLocalChecked());
+
+  std::string trace;

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

This stringify-stack-trace utility looks handy. In fact we do something similar
in other place(s). Could you move it to ScriptContext? (not the
exception-throwing part, which I'm a little uneasy about but I'll leave it alone
- just the stringify part).

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

Done.

+  v8::Local<v8::StackTrace> stack_trace =
+      v8::StackTrace::CurrentStackTrace(GetIsolate(), 10);
+  for (size_t i = 0; i < (size_t)stack_trace->GetFrameCount(); ++i) {

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

static_cast<size_t> not (size_t)?

[dcheng, 2015/06/17 22:55:09]

How about just using int instead of casting?

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

Done.

+    v8::Local<v8::StackFrame> frame = stack_trace->GetFrame(i);
+    CHECK(!frame.IsEmpty());
+    trace += base::StringPrintf(
+        "\n    at %s (%s:%d:%d)",
+        *v8::String::Utf8Value(frame->GetFunctionName()),
+        *v8::String::Utf8Value(frame->GetScriptName()),
+        frame->GetLineNumber(),
+        frame->GetColumn());
+  }
+  LOG(FATAL)
+      << "Invalid arguments to AutomationInternalCustomBindings function"
+      << trace;
+}
+
+bool AutomationInternalCustomBindings::GetNodeHelper(
+    const v8::FunctionCallbackInfo<v8::Value>& args,
+    TreeCache** out_cache,
+    ui::AXNode** out_node) {
+  if (args.Length() < 2 || !args[0]->IsNumber() || !args[1]->IsNumber()) {
+    ThrowInvalidArgumentsException(args);
+    return false;
+  }
+
+  int tree_id = args[0]->Int32Value();
+  int node_id = args[1]->Int32Value();
+
+  const auto& iter = tree_id_to_tree_cache_map_.find(tree_id);
+  if (iter == tree_id_to_tree_cache_map_.end())
+    return false;
+
+  TreeCache* cache = iter->second;
+  ui::AXNode* node = cache->tree.GetFromId(node_id);
+
+  if (out_cache)
+    *out_cache = cache;
+  if (out_node)
+    *out_node = node;
+
+  return node != nullptr;
+}
+
+bool AutomationInternalCustomBindings::GetAttributeHelper(
+    const v8::FunctionCallbackInfo<v8::Value>& args,
+    ui::AXNode** out_node,
+    std::string* out_attribute_name) {
+  if (args.Length() != 3 ||
+      !args[2]->IsString()) {
+    ThrowInvalidArgumentsException(args);
+    return false;
+  }
+
+  TreeCache* cache = nullptr;
+  if (!GetNodeHelper(args, &cache, out_node))
+    return false;
+
+  *out_attribute_name = *v8::String::Utf8Value(args[2]);
+  return true;
+}
+
+void AutomationInternalCustomBindings::SetReturnValueFromBaseValue(
+    const v8::FunctionCallbackInfo<v8::Value>& args,
+    const base::Value& value) {
+  v8::HandleScope handle_scope(GetIsolate());
+  v8::Context::Scope context_scope(context()->v8_context());
+  scoped_ptr<content::V8ValueConverter> converter(
+      content::V8ValueConverter::create());
+  v8::Local<v8::Value> v8_value =
+      converter->ToV8Value(&value, context()->v8_context());
+  args.GetReturnValue().Set(v8_value);
+}
+
+//
+// Handle accessibility events from the browser process.
+//
+
 void AutomationInternalCustomBindings::OnAccessibilityEvent(
     const ExtensionMsg_AccessibilityEventParams& params) {
-  // TODO(dmazzoni): finish implementing this.
+  int tree_id = params.tree_id;
+  TreeCache* cache;
+  auto iter = tree_id_to_tree_cache_map_.find(tree_id);
+  if (iter == tree_id_to_tree_cache_map_.end()) {
+    cache = new TreeCache();
+    cache->tab_id = -1;
+    cache->tree_id = params.tree_id;
+    cache->tree.SetDelegate(this);
+    tree_id_to_tree_cache_map_.insert(std::make_pair(tree_id, cache));
+    axtree_to_tree_cache_map_.insert(std::make_pair(&cache->tree, cache));
+  } else {
+    cache = iter->second;
+  }
+
+  cache->location_offset = params.location_offset;
+  if (!cache->tree.Unserialize(params.update)) {
+    LOG(FATAL) << cache->tree.error();
+    return;
+  }
+
+  api::automation_internal::AXEventParams event_params;
+  event_params.tree_id = params.tree_id;
+  event_params.target_id = params.id;
+  event_params.event_type = ToString(params.event_type);
+  base::ListValue args;
+  args.Append(event_params.ToValue());
+
+  v8::HandleScope handle_scope(GetIsolate());
+  v8::Context::Scope context_scope(context()->v8_context());
+  scoped_ptr<content::V8ValueConverter> converter(
+      content::V8ValueConverter::create());
+  v8::Local<v8::Value> v8_args =
+      converter->ToV8Value(&args, context()->v8_context());
+
+  DCHECK(v8_args->IsArray());
+  v8::Local<v8::Array> v8_args_array = v8_args.As<v8::Array>();
+  context()->DispatchEvent("automationInternal.onAccessibilityEvent",
+                           v8_args_array);
+}
+
+void AutomationInternalCustomBindings::OnNodeWillBeDeleted(ui::AXTree* tree,
+                                                           ui::AXNode* node) {
+  SendTreeChangeEvent(
+      api::automation::TREE_CHANGE_TYPE_NODEREMOVED,
+      tree, node);
+}
+
+void AutomationInternalCustomBindings::OnSubtreeWillBeDeleted(
+    ui::AXTree* tree,
+    ui::AXNode* node) {
+  // This isn't strictly needed, as OnNodeWillBeDeleted will already be
+  // called. We could send a JS event for this only if it turns out to
+  // be needed for something.
+}
+
+void AutomationInternalCustomBindings::OnNodeCreated(ui::AXTree* tree,
+                                                     ui::AXNode* node) {
+  // Not needed, this is called in the middle of an update so it's not
+  // safe to trigger JS from here. Wait for the notification in
+  // OnAtomicUpdateFinished instead.
+}
+
+void AutomationInternalCustomBindings::OnNodeChanged(ui::AXTree* tree,
+                                                     ui::AXNode* node) {
+  // Not needed, this is called in the middle of an update so it's not
+  // safe to trigger JS from here. Wait for the notification in
+  // OnAtomicUpdateFinished instead.
+}
+
+void AutomationInternalCustomBindings::OnAtomicUpdateFinished(
+    ui::AXTree* tree,
+    bool root_changed,
+    const std::vector<ui::AXTreeDelegate::Change>& changes) {
+  auto iter = axtree_to_tree_cache_map_.find(tree);
+  if (iter == axtree_to_tree_cache_map_.end())
+    return;
+
+  for (auto change : changes) {
+    ui::AXNode* node = change.node;
+    switch (change.type) {
+      case NODE_CREATED:
+        SendTreeChangeEvent(
+            api::automation::TREE_CHANGE_TYPE_NODECREATED,
+            tree, node);
+        break;
+      case SUBTREE_CREATED:
+        SendTreeChangeEvent(
+            api::automation::TREE_CHANGE_TYPE_SUBTREECREATED,
+            tree, node);
+        break;
+      case NODE_CHANGED:
+        SendTreeChangeEvent(
+            api::automation::TREE_CHANGE_TYPE_NODECHANGED,
+            tree, node);
+        break;
+    }
+  }
+}
+
+void AutomationInternalCustomBindings::SendTreeChangeEvent(
+    api::automation::TreeChangeType change_type,
+    ui::AXTree* tree,
+    ui::AXNode* node) {
+  auto iter = axtree_to_tree_cache_map_.find(tree);
+  if (iter == axtree_to_tree_cache_map_.end())
+    return;
+
+  int tree_id = iter->second->tree_id;
+  base::ListValue args;
+  args.AppendInteger(tree_id);
+  args.AppendInteger(node->id());
+  args.AppendString(ToString(change_type).c_str());
+
+  v8::HandleScope handle_scope(GetIsolate());
+  v8::Context::Scope context_scope(context()->v8_context());
+  scoped_ptr<content::V8ValueConverter> converter(
+      content::V8ValueConverter::create());

[not at google - send to devlin, 2015/06/17 21:14:47]

You should avoid dealing with base::Values as much as possible, if you can avoid
it, which I think you can. It adds a layer of inefficiency and churn, as does
dealing with V8ValueConverter.

I.e. if ultimately what you want is as v8::Value then construct it directly.

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

OK, done. I got rid of all uses of V8ValueConverter except one, because we
already get base::Values as input to OnAccessibilityEvent.

+  v8::Local<v8::Value> v8_args =
+      converter->ToV8Value(&args, context()->v8_context());
+
+  DCHECK(v8_args->IsArray());
+  v8::Local<v8::Array> v8_args_array = v8_args.As<v8::Array>();
+  context()->DispatchEvent("automationInternal.onTreeChange",
+                           v8_args_array);
 }
 
 }  // namespace extensions