[ServiceWorker] Fix ResourceFetcher::isControlledByServiceWorker to support HTMLImports.

Source/core/fetch/ResourceLoader.cpp

Index: Source/core/fetch/ResourceLoader.cpp
diff --git a/Source/core/fetch/ResourceLoader.cpp b/Source/core/fetch/ResourceLoader.cpp
index a7a670ae80ffee079aaf9cca98e2d8d56c49f0e6..daa5f6c077a4aeb9923254b6d70e65ed4ecec9b2 100644
--- a/Source/core/fetch/ResourceLoader.cpp
+++ b/Source/core/fetch/ResourceLoader.cpp
@@ -362,6 +362,7 @@ void ResourceLoader::didReceiveResponse(blink::WebURLLoader*, const blink::WebUR
     if (responseNeedsAccessControlCheck()) {
         if (response.wasFetchedViaServiceWorker()) {
             if (response.wasFallbackRequiredByServiceWorker()) {
+                ASSERT(m_fallbackRequestForServiceWorker);
                 m_loader->cancel();
                 m_loader.clear();
                 m_connectionState = ConnectionStateStarted;