Invalidate the text edit handler on selection events

This is necessary to make braille output work in menus. If a text edit handler is active, output gets delegated through that handler, skipping the output o f the current range.

BUG=657036
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2442583002
Cr-Commit-Position: refs/heads/master@{#427107}

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

@@ -428,6 +428,11 @@ DesktopAutomationHandler.prototype = {
    * @param {!AutomationEvent} evt
    */
   onSelection: function(evt) {
+    // Invalidate any previous editable text handler state since some nodes,
+    // like menuitems, can receive selection while focus remains on an editable
+    // leading to braille output routing to the editable.
+    this.textEditHandler_ = null;
+
     chrome.automation.getFocus(function(focus) {
       // Desktop tabs get "selection" when there's a focused webview during tab
       // switching.