Fix race condition in SafetyCheckUpdatesDelegateImpl

Likely pretty innocuous, but it's possible a GC could happen between the
two weakRef.get() calls.

Bug: None
Change-Id: I345fac7f72a70cef8aed80a834b47f3514d7f51a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2477048
Auto-Submit: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Andrey Zaytsev <andzaytsev@google.com>
Commit-Queue: Andrey Zaytsev <andzaytsev@google.com>
Cr-Commit-Position: refs/heads/master@{#818446}

chrome/android/java/src/org/chromium/chrome/browser/safety_check/SafetyCheckUpdatesDelegateImpl.java

@@ -68,8 +68,9 @@ public class SafetyCheckUpdatesDelegateImpl implements SafetyCheckUpdatesDelegat
             int status = mOmaha.checkForUpdates();
             // Post the results back to the UI thread.
             PostTask.postTask(UiThreadTaskTraits.DEFAULT, () -> {
-                if (statusCallback.get() != null) {
-                    statusCallback.get().onResult(convertOmahaUpdateStatus(status));
+                Callback<Integer> strongRef = statusCallback.get();
+                if (strongRef != null) {
+                    strongRef.onResult(convertOmahaUpdateStatus(status));
                 }
             });
         });