Bug 1187851 patch 5 - Make dynamic changes to perspective change fixed position containing block for descendants. r=roc

--HG--
extra : commitid : C2mD45KoQLU

layout/reftests/w3c-css/submitted/transforms/reftest.list

@@ -1,4 +1,4 @@
 == transform-containing-block-dynamic-1a.html containing-block-dynamic-1-ref.html
 == transform-containing-block-dynamic-1b.html containing-block-dynamic-1-ref.html
-fails == perspective-containing-block-dynamic-1a.html containing-block-dynamic-1-ref.html # bug 1187851
-fails == perspective-containing-block-dynamic-1b.html containing-block-dynamic-1-ref.html # bug 1187851
+== perspective-containing-block-dynamic-1a.html containing-block-dynamic-1-ref.html
+== perspective-containing-block-dynamic-1b.html containing-block-dynamic-1-ref.html

layout/style/nsStyleStruct.cpp

@@ -2844,6 +2844,11 @@ nsChangeHint nsStyleDisplay::CalcDifference(const nsStyleDisplay& aOther) const
         break;
       }
 
+    if (HasPerspectiveStyle() != aOther.HasPerspectiveStyle()) {
+      // A change from/to being a containing block for position:fixed.
+      NS_UpdateHint(hint, nsChangeHint_UpdateContainingBlock);
+    }
+
     if (mChildPerspective != aOther.mChildPerspective ||
         mTransformStyle != aOther.mTransformStyle ||
         mTransformBox != aOther.mTransformBox)