components: Introduce AlarmTimer class and use it for GCM heartbeat

components/gcm_driver/gcm_client_impl.cc

Index: components/gcm_driver/gcm_client_impl.cc
diff --git a/components/gcm_driver/gcm_client_impl.cc b/components/gcm_driver/gcm_client_impl.cc
index fa968a0e9a08a6a24202f7d4bc21a828762ecc8d..2b750038a6ff753fa303076028670b07e89de704 100644
--- a/components/gcm_driver/gcm_client_impl.cc
+++ b/components/gcm_driver/gcm_client_impl.cc
@@ -16,6 +16,7 @@
 #include "base/strings/stringprintf.h"
 #include "base/time/default_clock.h"
 #include "components/gcm_driver/gcm_backoff_policy.h"
+#include "components/timer/alarm_timer.h"
 #include "google_apis/gcm/base/encryptor.h"
 #include "google_apis/gcm/base/mcs_message.h"
 #include "google_apis/gcm/base/mcs_util.h"
@@ -192,12 +193,16 @@ scoped_ptr<MCSClient> GCMInternalsBuilder::BuildMCSClient(
     ConnectionFactory* connection_factory,
     GCMStore* gcm_store,
     GCMStatsRecorder* recorder) {
-  return make_scoped_ptr<MCSClient>(
-      new MCSClient(version,
-                    clock,
-                    connection_factory,
-                    gcm_store,
-                    recorder));
+  scoped_ptr<MCSClient> client(
+      new MCSClient(version, clock, connection_factory, gcm_store, recorder));
+
+#if defined(OS_CHROMEOS)
+  client->SetHeartbeatTimer(
+      make_scoped_ptr(new timer::AlarmTimer(true, /* retain user task */
+                                            false /* non-repeating */)));
+#endif
+
+  return client.Pass();
 }
 
 scoped_ptr<ConnectionFactory> GCMInternalsBuilder::BuildConnectionFactory(