Use an enum for ChromeVox queue mode.

chrome/browser/resources/chromeos/chromevox/chromevox/background/options.js

Index: chrome/browser/resources/chromeos/chromevox/chromevox/background/options.js
diff --git a/chrome/browser/resources/chromeos/chromevox/chromevox/background/options.js b/chrome/browser/resources/chromeos/chromevox/chromevox/background/options.js
index 8ba469e2102b9e8522f074a1764915284b757576..3126d8ed7986d58586ec215423e3ba3a555e156f 100644
--- a/chrome/browser/resources/chromeos/chromevox/chromevox/background/options.js
+++ b/chrome/browser/resources/chromeos/chromevox/chromevox/background/options.js
@@ -289,7 +289,8 @@ cvox.OptionsPage.addKeys = function() {
         // Indicate error and instructions excluding tab.
         if (evt.keyCode != 9) {
           cvox.OptionsPage.speak(
-              cvox.ChromeVox.msgs.getMsg('modifier_entry_error'), 0, {});
+              cvox.ChromeVox.msgs.getMsg('modifier_entry_error'),
+              cvox.QueueMode.FLUSH, {});
         }
         this.modifierSeq_ = null;
       } else {
@@ -555,7 +556,7 @@ cvox.OptionsPage.hidePlatformSpecifics = function() {
  * Calls a {@code cvox.TtsInterface.speak} method in the background page to
  * speak an utterance.  See that method for further details.
  * @param {string} textString The string of text to be spoken.
- * @param {number=} queueMode The queue mode to use.
+ * @param {cvox.QueueMode=} queueMode The queue mode to use.

[Peter Lundblad, 2014/09/29 13:51:03]

Should we make this required for consistency?

[dmazzoni, 2014/09/30 22:01:19]

Done.

  * @param {Object=} properties Speech properties to use for this utterance.
  */
 cvox.OptionsPage.speak = function(textString, queueMode, properties) {