Fix invalid vptr reference in LazyThreadControllerForTest::RestoreDefaultTaskRunner()

This was causing extensions_unittests to fail under UBSan, see bug.

Bug: 903339
Change-Id: Ie7d80297d85668e3ba72d0c92467bcf6975fce19
Reviewed-on: https://chromium-review.googlesource.com/c/1326508
Commit-Queue: Hans Wennborg <hans@chromium.org>
Commit-Queue: Alexander Timin <altimin@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606521}

base/task/sequence_manager/test/lazy_thread_controller_for_test.cc

@@ -119,7 +119,10 @@ void LazyThreadControllerForTest::SetDefaultTaskRunner(
 
 void LazyThreadControllerForTest::RestoreDefaultTaskRunner() {
   pending_default_task_runner_ = nullptr;
-  if (HasMessageLoop() && message_loop_->IsBoundToCurrentThread())
+  // We can't use message_loop_->IsBoundToCurrentThread as |message_loop_|
+  // might be deleted.
+  if (HasMessageLoop() &&
+      MessageLoopCurrent::Get()->ToMessageLoopDeprecated() == message_loop_)
     ThreadControllerImpl::RestoreDefaultTaskRunner();
 }