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 747 matching lines @@
     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.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.
+    // Next, see if an ancestor of both |start| and |end| is focusable.
+    var startAncestors = AutomationUtil.getAncestors(start);
+    var endAncestors = AutomationUtil.getAncestors(end);
+    var commonAncestorCount = (start == end ? startAncestors.length :
+        AutomationUtil.getDivergence(startAncestors, endAncestors));

[David Tseng, 2016/10/27 01:09:50]

As mentioned, AutomationUtil.getLeastCommonAncestor and then walk up.

[dmazzoni, 2016/10/27 06:27:27]

Done.

+
+    for (var i = commonAncestorCount - 1; i >= 0; --i) {

[David Tseng, 2016/10/27 01:09:50]

Thanks for doing this, but I don't really like the way this looks after
reconsidering.
- focusing root web areas blurs focus
- this messes up tab order. Example:
Suppose you have a toolbar (focusable) with 3 items. Two buttons and a text node
in that order. Object nav to the text. This would trigger a focus on the
toolbar. Tabbing at that point would move starting from the toolbar and onto the
first button. This goes for just about anything that's focusable with
descendants that are also focusable.

[dmazzoni, 2016/10/27 03:59:25]

OK, what if we limit it to just links, and text fields?

I think if you navigate to content inside of a link or inside
of a contenteditable I'd expect it to get focus.

I understand your concern about containers like toolbars, so maybe we could
just special-case the roles that make sense.

[dmazzoni, 2016/10/27 06:27:27]

Switched to just links within the same frame, that seem reasonable?

+      var ancestor = startAncestors[i];
+      if (isFocusable(ancestor)) {
+        if (!ancestor.state.focused)
+          ancestor.focus();
+        return;
+      }
+    }
+
+    // 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