AU: Try delta updates first, then full updates

Also, some bug fixes.

Review URL: http://codereview.chromium.org/492008
diff --git a/update_check_action_unittest.cc b/update_check_action_unittest.cc
index 723fc22..417a47e 100644
--- a/update_check_action_unittest.cc
+++ b/update_check_action_unittest.cc
@@ -54,7 +54,7 @@
         expected_success_(true) {}
   virtual ~UpdateCheckActionTestProcessorDelegate() {
   }
-  virtual void ProcessingDone(const ActionProcessor* processor) {
+  virtual void ProcessingDone(const ActionProcessor* processor, bool success) {
     ASSERT_TRUE(loop_);
     g_main_loop_quit(loop_);
   }