[HTML Imports] Implement "load" and "error" events.

Source/core/loader/cache/FetchRequest.h

Index: Source/core/loader/cache/FetchRequest.h
diff --git a/Source/core/loader/cache/FetchRequest.h b/Source/core/loader/cache/FetchRequest.h
index fb878f7233697d59b6d382dcff0cca531ff70fb6..974fff2b36b378abb5a175ac06d823783f7f33c2 100644
--- a/Source/core/loader/cache/FetchRequest.h
+++ b/Source/core/loader/cache/FetchRequest.h
@@ -47,6 +47,7 @@ public:
 
     ResourceRequest& mutableResourceRequest() { return m_resourceRequest; }
     const ResourceRequest& resourceRequest() const { return m_resourceRequest; }
+    const KURL& url() const { return m_resourceRequest.url(); }
     const String& charset() const { return m_charset; }
     void setCharset(const String& charset) { m_charset = charset; }
     const ResourceLoaderOptions& options() const { return m_options; }