Initial support for native accessibility in ARC

components/arc/common/accessibility_helper.mojom

 // Copyright 2017 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.
 
 // Next MinVersion: 1
 
 module arc.mojom;
 
 import "screen_rect.mojom";
 
 // AccessibilityEventType is a enum which corresponds to event types of
 // AccessibilityEvent in Android.
 // https://developer.android.com/reference/android/view/accessibility/AccessibilityEvent.html
 [Extensible]
 enum AccessibilityEventType {
   VIEW_FOCUSED,
 };
 
 // AccessibilityNodeInfoData is a struct to contain info of
 // AccessibilityNodeInfo in Android.
 // https://developer.android.com/reference/android/view/accessibility/AccessibilityNodeInfo.html
 struct AccessibilityNodeInfoData {
   ScreenRect boundsInScreen;
+  int32 id;
+  string contentDescription;
+  string text;
+  string className;
+  array<int32> childIds;
+};
+
+// AccessibilityEventData is a struct to contain info of
+// AccessibilityEvent in Android.
+// https://developer.android.com/reference/android/view/accessibility/AccessibilityEvent.html
+struct AccessibilityEventData {
+  AccessibilityEventType eventType;
+  int32 sourceId;
+  array<AccessibilityNodeInfoData> nodeData;

[yawano, 2017/02/08 11:11:27]

What data is expected to this nodeData field? Is this corresponding to
AccessibilityEvent.getSource()? Will the whole tree of AccessibilityNodeInfo be
returned? Or just the subtree from the node of AccessibilityEvent.getSource()? 

[David Tseng, 2017/02/08 18:49:26]

The whole tree rooted at the source node's root will be contained in the
nodeData field.

See the latest patchset, which is the one ready for review, for more details.

In that cl, there's a filter to only receive focus events -- in which case this
nodeData will only contain the focus node data.

For the "ALL" filter, we will start by sending the entire tree for every event.
I don't want to prematurely optimize especially when this is all hidden behind a
flag. We can then look at making optimization e.g. only sending tree contents on
window content changed events (which would require we keep more state in the
browser). Currently, besides the serializer, we're keeping no state.

 };
 
 // Next method ID: 1
 interface AccessibilityHelperHost {
   // OnAccessibilityEvent is called when a converted Android accessibility event
   // is sent from Android.
-  OnAccessibilityEvent@0(AccessibilityEventType eventType,
-                         AccessibilityNodeInfoData? eventSource);
+  OnAccessibilityEvent@0(AccessibilityEventData eventData);
 };
 
 // Next method ID: 1
 interface AccessibilityHelperInstance {
   Init@0(AccessibilityHelperHost host);
 };