Bug 1387912 - Add missing #include to dom/canvas/ImageBitmap.h, to avoid build fragility (unified-compilation dependency. r=jrmuizel a=stability

MozReview-Commit-ID: 3ptkeF67jB2

--HG--
extra : amend_source : 81ecd6836ffed785617bc1f0c6a427c3148d586d
extra : transplant_source : %22sO%3DK%602S%F6%E9%BA%1BO%F9%BD6%E4%A77%12

dom/canvas/ImageBitmap.h

@@ -13,6 +13,7 @@
 #include "mozilla/gfx/Rect.h"
 #include "mozilla/Maybe.h"
 #include "mozilla/UniquePtr.h"
+#include "gfxTypes.h" // for gfxAlphaType
 #include "nsCycleCollectionParticipant.h"
 
 struct JSContext;