Fixes regressions in ChromeVox since revision to event stream

ChromeVox used a tree path based recovery strategy to work around issues on google.com
(see crbug.com/885244).
https://chromium-review.googlesource.com/c/chromium/src/+/1534283

As of
https://chromium-review.googlesource.com/c/chromium/src/+/1889165
the above issue seems to have been resolved without using tree path based recovery. Revert ChromeVox back to using ordinary ancestry recovery.

Bug: 945708
Change-Id: I6b8599d2daf42bc1bad036b911fa77d802e66451
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1539262Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Commit-Queue: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#644481}

chrome/browser/resources/chromeos/chromevox/cvox2/background/cursors.js

@@ -103,7 +103,7 @@ cursors.Cursor = function(node, index) {
   /** @type {number} @private */
   this.index_ = index;
   /** @type {RecoveryStrategy} */
-  this.recovery_ = new TreePathRecoveryStrategy(node);
+  this.recovery_ = new AncestryRecoveryStrategy(node);
 };
 
 /**