AU: Start an UpdateAttempter unit test suite.

This increases the UpdateAttmpter line coverage to almost 40%. More is needed
but this is a good starting point / checkpoint. Also some UpdateCheckScheduler
unit test cleanup.

BUG=6243
TEST=unit tests, gmerge on device

Change-Id: I39c80de3f18095c4a28cb36ab868bed6d7073824

Review URL: http://codereview.chromium.org/3259011
diff --git a/download_action.h b/download_action.h
index 189121b..c0c36f1 100644
--- a/download_action.h
+++ b/download_action.h
@@ -87,6 +87,7 @@
                              const char* bytes, int length);
   virtual void TransferComplete(HttpFetcher *fetcher, bool successful);
 
+  DownloadActionDelegate* delegate() const { return delegate_; }
   void set_delegate(DownloadActionDelegate* delegate) {
     delegate_ = delegate;
   }