Use setSequentialFocusNavigationStartingPoint in ChromeVox

chrome/browser/resources/chromeos/chromevox/cvox2/background/background.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.
 
 /**
  * @fileoverview The entry point for all ChromeVox2 related code for the
  * background page.
  */
 
 goog.provide('Background');
@@ skipping 753 matching lines @@
     var start = range.start.node;
     var end = range.end.node;
     if (start.state.focused || end.state.focused)
       return;
 
     // Iframes, when focused, causes the child webArea to fire focus
     // event.  This can result in getting stuck when navigating
     // backward.
     var isFocusable = function(node) {
       return node.role != RoleType.iframe &&
+          node.role != RoleType.rootWebArea &&
           node.state.focusable &&
-          !node.state.focused &&
           !AutomationPredicate.structuralContainer(node);
     };
+
+    // First, try to focus the start or end node.
     if (isFocusable(start)) {
-      start.focus();
+      if (!start.state.focused)
+        start.focus();
       return;
-    }
-    if (isFocusable(end)) {
-      end.focus();
+    } else if (isFocusable(end)) {
+      if (!end.state.focused)
+        end.focus();
       return;
     }
 
-    // TODO(dmazzoni): Set sequential focus.
+    // If a common ancestor of |start| and |end| is a link, focus that.
+    var ancestor = AutomationUtil.getLeastCommonAncestor(start, end);
+    while (ancestor && ancestor.root == start.root) {

[David Tseng, 2016/10/27 17:03:18]

Counter example:

<a href="test">
  <button>ok</button>
  <p>with ChromeVox range here call focus on my parent</p>
<button>cancel</button>
  </a>

The correct way to focus here I think is to walk backwards in dfs order until
you find a focusable node. If that focusable node is an ancestor of the current
node/range, then focus it.

[dmazzoni, 2016/10/27 19:42:50]

As discussed in person, NVDA behaves the same for this example
so I don't think it'd be wrong.

As discussed, I'm changing the code to only focus links and
controls. That avoids problems with cases like focusable
toolbars or focusable divs.

+      if (ancestor.role == RoleType.link && ancestor.state.focusable) {
+        if (!ancestor.state.focused)
+          ancestor.focus();
+        return;
+      }
+      ancestor = ancestor.parent;
+    }
+
+    // If nothing is focusable, set the sequential focus navigation starting
+    // point, which ensures that the next time you press Tab, you'll reach
+    // the next or previous focusable node from |start|.
+    start.setSequentialFocusNavigationStartingPoint();
   }
 };
 
 /**
  * Converts a list of globs, as used in the extension manifest, to a regular
  * expression that matches if and only if any of the globs in the list matches.
  * @param {!Array<string>} globs
  * @return {!RegExp}
  * @private
  */
 Background.globsToRegExp_ = function(globs) {
   return new RegExp('^(' + globs.map(function(glob) {
     return glob.replace(/[.+^$(){}|[\]\\]/g, '\\$&')
         .replace(/\*/g, '.*')
         .replace(/\?/g, '.');
   }).join('|') + ')$');
 };
 
 new Background();
 
 });  // goog.scope