HTML Imports: Teach preloader about HTML Imports.

Source/core/testing/Internals.cpp

Index: Source/core/testing/Internals.cpp
diff --git a/Source/core/testing/Internals.cpp b/Source/core/testing/Internals.cpp
index d00a9f1ba3b55d0baefd64061a830747ac46493c..7eb480af53468048c2c1f77ec72d17f1ba16526f 100644
--- a/Source/core/testing/Internals.cpp
+++ b/Source/core/testing/Internals.cpp
@@ -296,7 +296,13 @@ unsigned Internals::needsLayoutCount(ExceptionState& exceptionState) const
 
 bool Internals::isPreloaded(const String& url)
 {
-    Document* document = contextDocument();
+    return isPreloadedBy(url, contextDocument());
+}
+
+bool Internals::isPreloadedBy(const String& url, Document* document)
+{
+    if (!document)
+        return false;
     return document->fetcher()->isPreloaded(url);
 }