Add support for gcm_sender_id in Manifest.

content/browser/manifest/manifest_manager_host.cc

Index: content/browser/manifest/manifest_manager_host.cc
diff --git a/content/browser/manifest/manifest_manager_host.cc b/content/browser/manifest/manifest_manager_host.cc
index ebab903d0956d3a04b2b0ba3cbaaba56dc103c60..962189fff3d86ec5a1773361f66b3e04dea46381 100644
--- a/content/browser/manifest/manifest_manager_host.cc
+++ b/content/browser/manifest/manifest_manager_host.cc
@@ -119,6 +119,10 @@ void ManifestManagerHost::OnRequestManifestResponse(
                                                Manifest::kMaxIPCStringLength),
         manifest.icons[i].type.is_null());
   }
+  manifest.gcm_sender_id = base::NullableString16(
+        manifest.gcm_sender_id.string().substr(
+            0, Manifest::kMaxIPCStringLength),
+        manifest.gcm_sender_id.is_null());
 
   callback->Run(manifest);
   callbacks->Remove(request_id);