Bail out of maybeShareOfflinePage on uninitialized Tab

We now enforce that Tab attributes cannot be acquired
on an uninitialized Tab. If we don't bail out here
we will attempt to pull the title or url off an uninitialized
Tab leading to a crash.

Bug: 1133038
Change-Id: Idd39105dc47ac208b5e9e33144996f3643fec25c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2436326Reviewed-by: Peter Williamson <petewil@chromium.org>
Commit-Queue: David Maunder <davidjm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811810}

chrome/android/java/src/org/chromium/chrome/browser/offlinepages/OfflinePageUtils.java

@@ -394,7 +394,7 @@ public class OfflinePageUtils {
      *                      afterwards via PostTask.
      */
     public static void maybeShareOfflinePage(Tab tab, final Callback<ShareParams> shareCallback) {
-        if (tab == null) {
+        if (tab == null || !tab.isInitialized()) {
             shareCallback.onResult(null);
             return;
         }