shill: Propagate Cellular Activate call errors to the DBus caller.

BUG=chromium-os:19547
TEST=unit tests

Change-Id: I2a0f889f0863c299c3f3ac006a6df5a608407881
Reviewed-on: http://gerrit.chromium.org/gerrit/6616
Reviewed-by: Darin Petkov <petkov@chromium.org>
Tested-by: Darin Petkov <petkov@chromium.org>
diff --git a/error.cc b/error.cc
index c9799ba..030e598 100644
--- a/error.cc
+++ b/error.cc
@@ -49,7 +49,7 @@
   Populate(type);
 }
 
-Error::Error(Type type, const std::string &message) {
+Error::Error(Type type, const string &message) {
   Populate(type, message);
 }
 
@@ -59,7 +59,7 @@
   Populate(type, GetDefaultMessage(type));
 }
 
-void Error::Populate(Type type, const std::string &message) {
+void Error::Populate(Type type, const string &message) {
   CHECK(type < kNumErrors) << "Error type out of range: " << type;
   type_ = type;
   message_ = message;