shill: implement Manager.GetService (error-case only)

BUG=chromium-os:20254
TEST=unittests, WiFiManager/000_SSID_Length_Limit

this gives us enough to pass the autotest for
network_WiFiManager/000_SSID_Length_Limit.

Change-Id: Ib0305e707d2203327d846be3e0b206033d6a884a
Reviewed-on: http://gerrit.chromium.org/gerrit/7567
Commit-Ready: mukesh agrawal <quiche@chromium.org>
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Tested-by: mukesh agrawal <quiche@chromium.org>
diff --git a/error.h b/error.h
index dc2ab19..c1fb2b1 100644
--- a/error.h
+++ b/error.h
@@ -49,9 +49,9 @@
   void Populate(Type type);  // Uses the default message for |type|.
   void Populate(Type type, const std::string &message);
 
-  // Sets the DBus |error| to this error if it's failure. Leaves |error|
-  // unchanged otherwise.
-  void ToDBusError(::DBus::Error *error) const;
+  // Sets the DBus |error| and returns true if Error represents failure.
+  // Leaves |error| unchanged, and returns false, otherwise.
+  bool ToDBusError(::DBus::Error *error) const;
 
   Type type() const { return type_; }
   const std::string &message() const { return message_; }