shill: Broadcast changes of CellularService's ActivationState property.

BUG=chromium-os:25011
TEST=tested on device

Change-Id: Iaf5e38dc7402312ac056c9a39718085c3f236ed4
Reviewed-on: https://gerrit.chromium.org/gerrit/14056
Tested-by: Darin Petkov <petkov@chromium.org>
Reviewed-by: Eric Shienbrood <ers@chromium.org>
Commit-Ready: Darin Petkov <petkov@chromium.org>
diff --git a/cellular_service.cc b/cellular_service.cc
index dbd6e70..7138952 100644
--- a/cellular_service.cc
+++ b/cellular_service.cc
@@ -76,6 +76,14 @@
   return cellular_->GetRpcIdentifier();
 }
 
+void CellularService::SetActivationState(const string &state) {
+  if (state == activation_state_) {
+    return;
+  }
+  activation_state_ = state;
+  adaptor()->EmitStringChanged(flimflam::kActivationStateProperty, state);
+}
+
 void CellularService::SetNetworkTechnology(const string &technology) {
   if (technology == network_technology_) {
     return;