shill: Support for GSM network scanning.

This is mostly placeholder code since synchronous calls will cause crashes due
to timeouts.

BUG=chromium-os:19805
TEST=unit tests

Change-Id: I7ad07d6274b19b39d7955ee256c6928c9f1ce5a1
Reviewed-on: http://gerrit.chromium.org/gerrit/7895
Commit-Ready: Darin Petkov <petkov@chromium.org>
Reviewed-by: Darin Petkov <petkov@chromium.org>
Tested-by: Darin Petkov <petkov@chromium.org>
diff --git a/device.cc b/device.cc
index 13426df..1a16245 100644
--- a/device.cc
+++ b/device.cc
@@ -146,8 +146,12 @@
           << std::dec << std::noshowbase;
 }
 
-void Device::Scan() {
+void Device::Scan(Error *error) {
   VLOG(2) << "Device " << link_name_ << " scan requested.";
+  const string kMessage = "Device doesn't support scan.";
+  LOG(ERROR) << kMessage;
+  CHECK(error);
+  error->Populate(Error::kNotSupported, kMessage);
 }
 
 void Device::RegisterOnNetwork(const std::string &network_id, Error *error) {