[TTS] Update last assert in CSearchTabHelper

Speculative fix for an assert reported by a developer.
Update an overly aggressive assert recently landed in
ContextualSearchTabHelper when reparenting.

BUG=783225, 775813

Change-Id: Ib8f54e0b5bfcf8dde785e0c25098771b21c1b420
Reviewed-on: https://chromium-review.googlesource.com/764667Reviewed-by: Theresa <twellington@chromium.org>
Commit-Queue: Donn Denman <donnd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#515755}

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

@@ -206,7 +206,7 @@ public class ContextualSearchTabHelper
      * @param cvc The content view core to attach the gesture state listener to.
      */
     private void addContextualSearchHooks(ContentViewCore cvc) {
-        assert mTab.getContentViewCore() == cvc;
+        assert mTab.getContentViewCore() == null || mTab.getContentViewCore() == cvc;
         ContextualSearchManager contextualSearchManager = getContextualSearchManager(mTab);
         if (mGestureStateListener == null && contextualSearchManager != null) {
             mGestureStateListener = contextualSearchManager.getGestureStateListener();