Add ref count to service workers for extension API.

extensions/common/constants.h

Index: extensions/common/constants.h
diff --git a/extensions/common/constants.h b/extensions/common/constants.h
index d3f0b5320983e6a5adfaca8c5a237319563fd881..4e1ef6a974a8733d9034ea4e4bb4f5c30704759d 100644
--- a/extensions/common/constants.h
+++ b/extensions/common/constants.h
@@ -104,6 +104,11 @@ extern const char kAuthUserQueryKey[];
 extern const char kMimeTypeJpeg[];
 extern const char kMimeTypePng[];
 
+// TODO(lazyboy): This is a hack and it is copied from service_worker_types.cc,
+// which is not available to extensions/ code. Move the constant to
+// content/public/common.
+extern const int64_t kInvalidServiceWorkerVersionId;
+
 // The extension id of the Web Store component application.
 extern const char kWebStoreAppId[];