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

Source/core/html/HTMLImportLoaderClient.h

Index: Source/core/html/HTMLImportLoaderClient.h
diff --git a/Source/core/loader/UniqueIdentifier.cpp b/Source/core/html/HTMLImportLoaderClient.h
similarity index 88%
copy from Source/core/loader/UniqueIdentifier.cpp
copy to Source/core/html/HTMLImportLoaderClient.h
index 0ad56563e3e214a67acd8c53decb085ad4250cb9..0cac67f2dca404e039df1785c07743cedbc34add 100644
--- a/Source/core/loader/UniqueIdentifier.cpp
+++ b/Source/core/html/HTMLImportLoaderClient.h
@@ -28,17 +28,17 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include "config.h"
-#include "core/loader/UniqueIdentifier.h"
+#ifndef HTMLImportLoaderClient_h
+#define HTMLImportLoaderClient_h
 
 namespace WebCore {
 
-static unsigned long s_uniqueIdentifier = 0;
-
-unsigned long createUniqueIdentifier()
-{
-    return ++s_uniqueIdentifier;
-}
+class HTMLImportLoaderClient {
+public:
+    virtual ~HTMLImportLoaderClient() { }
+    virtual void didFinish() = 0;
+};
 
 } // namespace WebCore
 
+#endif // HTMLImportLoaderClient_h