Only provide tab creation output for highlighted tabs

AX-Relnotes: n/a
Change-Id: If9025b31fb1fceb89e4c691cc89f632eca632de8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2466137Reviewed-by: Roman Sorokin [CET] <rsorokin@chromium.org>
Commit-Queue: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816617}

chrome/browser/resources/chromeos/accessibility/chromevox/background/tabs_api_handler.js

@@ -54,6 +54,10 @@ TabsApiHandler = class {
    * @param {Object} tab
    */
   onCreated(tab) {
+    if (!tab.highlighted) {
+      return;
+    }
+
     if (TabsApiHandler.shouldOutputSpeechAndBraille) {
       ChromeVox.tts.speak(
           this.msg_('chrome_tab_created'), QueueMode.FLUSH,