Change assert in RecentTabsPage.destroy(). It always failed when the...

Change assert in RecentTabsPage.destroy(). It always failed when the RecentTabsPage was closed without opening a recent tab.

BUG=

Review-Url: https://codereview.chromium.org/2595933002
Cr-Commit-Position: refs/heads/master@{#442885}

chrome/android/java/src/org/chromium/chrome/browser/ntp/RecentTabsPage.java

@@ -165,7 +165,7 @@ public class RecentTabsPage
 
     @Override
     public void destroy() {
-        assert getView().getParent() == null : "Destroy called before removed from window";
+        assert !mIsAttachedToWindow : "Destroy called before removed from window";
         mRecentTabsManager.destroy();
         mRecentTabsManager = null;
         mAdapter.notifyDataSetInvalidated();