Use a predicate that isn't so granular during continuous read.

chrome/browser/resources/chromeos/chromevox/chromevox/injected/init_document.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 Initializes the injected content script on the document.
  *
  * NOTE(deboer): This file will automatically initialize ChromeVox.  If you can
  * control when ChromeVox starts, consider using cvox.InitGlobals instead.
  *
@@ skipping 27 matching lines @@
  * Maximum retry timeout for initialization.  Note that exponential backoff
  * used, so the actual time before giving up is about twice this number.
  * @const {number}
  * @private
  */
 cvox.ChromeVox.MAX_INIT_TIMEOUT_ = 30000;
 
 
 /**
  * Flag indicating if ChromeVox Classic is enabled based on the Next
- * background page. Initializes to true for non-top level
- * (i.e. iframes) windows. For top level windows, left undefined and
- * set when background page replies.
+ * background page which sends the state at page load.
  * @type {boolean|undefined}
  * @private
  */
-cvox.ChromeVox.isClassicEnabled_ = window.top == window ? undefined : true;

[dmazzoni, 2016/01/20 06:31:05]

Is this from a different patch?

+cvox.ChromeVox.isClassicEnabled_ = undefined;
 
 
 /**
  * Call the init function later, safely.
  * @param {string} reason A developer-readable string to log to the console
  *    explaining why we're trying again.
  * @private
  */
 cvox.ChromeVox.recallInit_ = function(reason) {
   if (cvox.ChromeVox.initTimeout_ > cvox.ChromeVox.MAX_INIT_TIMEOUT_) {
-    window.console.log(reason +
-        ' Taking too long - giving up.');
-    return;
+    if (cvox.ChromeVox.isClassicEnabled_ !== undefined) {
+      window.console.log(reason +
+          ' Taking too long - giving up.');
+      return;
+    } else {
+      // Default to enabling classic after the timeout.
+      cvox.ChromeVox.isClassicEnabled_ = true;
+    }
   }
   window.console.log(reason +
                      ' Will try again in ' +
                      cvox.ChromeVox.initTimeout_ + 'ms');
   cvox.ChromeVox.initTimer_ = window.setTimeout(
       cvox.ChromeVox.initDocument,
       cvox.ChromeVox.initTimeout_);
   cvox.ChromeVox.initTimeout_ *= 2;
 };
 
@@ skipping 78 matching lines @@
     cvox.ChromeVox.isClassicEnabled_ = msg['isClassicEnabled'];
   }
 });
 
 cvox.ExtensionBridge.addDisconnectListener(function() {
   if (cvox.ChromeVox.initTimer_ > 0) {
     window.clearTimeout(cvox.ChromeVox.initTimer_);
     cvox.ChromeVox.initTimer_ = 0;
   }
 });