[Android Webapp Refactor] Remove useless null check in WebappActivity#restoreTab()

WebappActivity#getActivityDirectory() never returns null.

Change-Id: Ie6b131677e6a69a49b8c72713235dc0891f5dbe2
Reviewed-on: https://chromium-review.googlesource.com/c/1340371Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Commit-Queue: Peter Kotwicz <pkotwicz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608851}

chrome/android/java/src/org/chromium/chrome/browser/webapps/WebappActivity.java

@@ -355,7 +355,7 @@ public class WebappActivity extends SingleTabActivity {
     protected Tab restoreTab(Bundle savedInstanceState) {
         int tabId = getSavedInstanceState().getInt(BUNDLE_TAB_ID, Tab.INVALID_TAB_ID);
 
-        if (tabId == Tab.INVALID_TAB_ID || getActivityDirectory() == null) return null;
+        if (tabId == Tab.INVALID_TAB_ID) return null;
 
         TabState tabState = TabState.restoreTabState(getActivityDirectory(), tabId);
         if (tabState == null) return null;