Fix Chrome linker errors in GN build.

components/gcm_driver/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 static_library("gcm_driver") {
   sources = [
     "android/component_jni_registrar.cc",
     "android/component_jni_registrar.h",
     "default_gcm_app_handler.cc",
     "default_gcm_app_handler.h",
     "gcm_activity.cc",
     "gcm_activity.h",
     "gcm_app_handler.cc",
     "gcm_app_handler.h",
     "gcm_client.cc",
     "gcm_client.h",
     "gcm_client_factory.cc",
     "gcm_client_factory.h",
     "gcm_client_impl.cc",
     "gcm_client_impl.h",
+    "gcm_connection_observer.cc",
+    "gcm_connection_observer.h",
     "gcm_driver.cc",
     "gcm_driver.h",
     "gcm_driver_android.cc",
     "gcm_driver_android.h",
     "gcm_driver_desktop.cc",
     "gcm_driver_desktop.h",
     "gcm_stats_recorder_impl.cc",
     "gcm_stats_recorder_impl.h",
     "system_encryptor.cc",
     "system_encryptor.h",
@@ skipping 46 matching lines @@
       "fake_gcm_client.cc",
       "fake_gcm_client.h",
       "fake_gcm_client_factory.cc",
       "fake_gcm_client_factory.h",
     ]
     deps -= [ "//google_apis/gcm" ]
   }
 }
 
 #TODO(GYP) gcm_driver_java gcm_driver_jni_headers