Make HistoryDBTask not refcounted, and ensure it's destroyed on its origin thread.

chrome/browser/history/top_sites_impl_unittest.cc

Index: chrome/browser/history/top_sites_impl_unittest.cc
diff --git a/chrome/browser/history/top_sites_impl_unittest.cc b/chrome/browser/history/top_sites_impl_unittest.cc
index 7d070561c85eb3b036484359e57b35866d739924..044f3bc2eeb80839338cf3ff56497ae1b95c572f 100644
--- a/chrome/browser/history/top_sites_impl_unittest.cc
+++ b/chrome/browser/history/top_sites_impl_unittest.cc
@@ -181,8 +181,9 @@ class TopSitesImplTest : public HistoryUnitTestBase {
   // Blocks the caller until history processes a task. This is useful if you
   // need to wait until you know history has processed a task.
   void WaitForHistory() {
-    history_service()->ScheduleDBTask(new WaitForHistoryTask(),
-                                      &history_tracker_);
+    history_service()->ScheduleDBTask(
+        scoped_ptr<history::HistoryDBTask>(new WaitForHistoryTask()),
+        &history_tracker_);
     base::MessageLoop::current()->Run();
   }