diff -r 000000000000 -r 6474c204b198 image/src/DecodeStrategy.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/image/src/DecodeStrategy.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,36 @@
+/* -*- 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/. */
+
+/** @file
+ * An enumeration used by RasterImage and Decoder to specify which 'strategy' to
+ * use for image decoding - synchronous or asynchronous.
+ */
+
+#ifndef mozilla_imagelib_DecodeStrategy_h_
+#define mozilla_imagelib_DecodeStrategy_h_
+
+namespace mozilla {
+namespace image {
+
+enum DecodeStrategy {
+  // DECODE_SYNC requests a synchronous decode, which will continue decoding
+  // frames as long as it has more source data. It returns to the caller only
+  // once decoding is complete (or until it needs more source data before
+  // continuing). Because DECODE_SYNC can involve allocating new imgFrames, it
+  // can only be run on the main thread.
+  DECODE_SYNC,
+
+  // DECODE_ASYNC requests an asynchronous decode, which will continue decoding
+  // until it either finishes a frame or runs out of source data. Because
+  // DECODE_ASYNC does not allocate new imgFrames, it can be safely run off the
+  // main thread. (And hence workers in the decode pool always use it.)
+  DECODE_ASYNC
+};
+
+} // namespace image
+} // namespace mozilla
+
+#endif