AU: propagate a deadline form the update check response to Chrome.

Currently, this is done through the file system.

BUG=3284
TEST=unit tests

Change-Id: I0e579ef6ccd7832ca22a248e71f2689c27159056

TBR=resubmitting due to git issues
diff --git a/omaha_response_handler_action.h b/omaha_response_handler_action.h
index 2845df5..25c57e0 100644
--- a/omaha_response_handler_action.h
+++ b/omaha_response_handler_action.h
@@ -27,6 +27,8 @@
 
 class OmahaResponseHandlerAction : public Action<OmahaResponseHandlerAction> {
  public:
+  static const char kDeadlineFile[];
+
   OmahaResponseHandlerAction(PrefsInterface* prefs)
       : prefs_(prefs),
         got_no_update_response_(false) {}