diff -r 000000000000 -r 6474c204b198 layout/style/nsICSSLoaderObserver.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/layout/style/nsICSSLoaderObserver.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,44 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* internal interface for observing CSS style sheet loads */
+
+#ifndef nsICSSLoaderObserver_h___
+#define nsICSSLoaderObserver_h___
+
+#include "nsISupports.h"
+
+#define NS_ICSSLOADEROBSERVER_IID     \
+{ 0x7eb90c74, 0xea0c, 0x4df5,       \
+{0xa1, 0x5f, 0x95, 0xf0, 0x6a, 0x98, 0xb9, 0x40} }
+
+class nsCSSStyleSheet;
+
+class nsICSSLoaderObserver : public nsISupports {
+public:
+  NS_DECLARE_STATIC_IID_ACCESSOR(NS_ICSSLOADEROBSERVER_IID)
+
+  /**
+   * StyleSheetLoaded is called after aSheet is marked complete and before any
+   * load events associated with aSheet are fired.
+   * @param aSheet the sheet that was loaded. Guaranteed to always be
+   *        non-null, even if aStatus indicates failure.
+   * @param aWasAlternate whether the sheet was an alternate.  This will always
+   *        match the value LoadStyleLink or LoadInlineStyle returned in
+   *        aIsAlternate if one of those methods were used to load the sheet,
+   *        and will always be false otherwise.
+   * @param aStatus is a success code if the sheet loaded successfully and a
+   *        failure code otherwise.  Note that successful load of aSheet
+   *        doesn't indicate anything about whether the data actually parsed
+   *        as CSS, and doesn't indicate anything about the status of any child
+   *        sheets of aSheet.
+   */
+  NS_IMETHOD StyleSheetLoaded(nsCSSStyleSheet* aSheet, bool aWasAlternate,
+                              nsresult aStatus) = 0;
+};
+
+NS_DEFINE_STATIC_IID_ACCESSOR(nsICSSLoaderObserver, NS_ICSSLOADEROBSERVER_IID)
+
+#endif // nsICSSLoaderObserver_h___