[TTS] Hide the panel when Talkback is enabled.

When the panel is showing and Talkback is enabled the panel
should be hidden.

BUG=787553

Change-Id: Ic98b347f7cff6dc931b952e9846968fbecc67eed
Reviewed-on: https://chromium-review.googlesource.com/830607Reviewed-by: Theresa <twellington@chromium.org>
Commit-Queue: Donn Denman <donnd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524514}

chrome/android/java/src/org/chromium/chrome/browser/contextualsearch/ContextualSearchManager.java

@@ -834,6 +834,7 @@ public class ContextualSearchManager
      */
     public void onAccessibilityModeChanged(boolean enabled) {
         mIsAccessibilityModeEnabled = enabled;
+        if (enabled) hideContextualSearch(StateChangeReason.UNKNOWN);
     }
 
     /**