Bug 1227766 patch 1 - Add flag for CSS properties that establish a containing block for fixed positioned elements. r=dholbert

layout/style/nsCSSPropList.h

@@ -1482,7 +1482,8 @@ CSS_PROP_DISPLAY(
     contain,
     Contain,
     CSS_PROPERTY_PARSE_VALUE |
-        CSS_PROPERTY_VALUE_PARSER_FUNCTION,
+        CSS_PROPERTY_VALUE_PARSER_FUNCTION |
+        CSS_PROPERTY_FIXPOS_CB,
     "layout.css.contain.enabled",
     // Does not affect parsing, but is needed for tab completion in devtools:
     VARIANT_HK | VARIANT_NONE,
@@ -3383,7 +3384,8 @@ CSS_PROP_DISPLAY(
     CSS_PROPERTY_PARSE_FUNCTION |
         CSS_PROPERTY_GETCS_NEEDS_LAYOUT_FLUSH |
         CSS_PROPERTY_CREATES_STACKING_CONTEXT |
-        CSS_PROPERTY_CAN_ANIMATE_ON_COMPOSITOR,
+        CSS_PROPERTY_CAN_ANIMATE_ON_COMPOSITOR |
+        CSS_PROPERTY_FIXPOS_CB,
     "",
     0,
     nullptr,
@@ -3428,7 +3430,8 @@ CSS_PROP_DISPLAY(
     perspective,
     Perspective,
     CSS_PROPERTY_PARSE_VALUE |
-        CSS_PROPERTY_CREATES_STACKING_CONTEXT,
+        CSS_PROPERTY_CREATES_STACKING_CONTEXT |
+        CSS_PROPERTY_FIXPOS_CB,
     "",
     VARIANT_NONE | VARIANT_INHERIT | VARIANT_LENGTH | VARIANT_POSITIVE_DIMENSION,
     nullptr,
@@ -3439,7 +3442,8 @@ CSS_PROP_DISPLAY(
     transform_style,
     TransformStyle,
     CSS_PROPERTY_PARSE_VALUE |
-        CSS_PROPERTY_CREATES_STACKING_CONTEXT,
+        CSS_PROPERTY_CREATES_STACKING_CONTEXT |
+        CSS_PROPERTY_FIXPOS_CB,
     "",
     VARIANT_HK,
     kTransformStyleKTable,
@@ -3967,7 +3971,8 @@ CSS_PROP_SVGRESET(
     filter,
     Filter,
     CSS_PROPERTY_PARSE_FUNCTION |
-        CSS_PROPERTY_CREATES_STACKING_CONTEXT,
+        CSS_PROPERTY_CREATES_STACKING_CONTEXT |
+        CSS_PROPERTY_FIXPOS_CB,
     "",
     0,
     nullptr,

layout/style/nsCSSProps.h

@@ -255,6 +255,13 @@ static_assert((CSS_PROPERTY_PARSE_PROPERTY_MASK &
 // CSS_PROP_LIST_EXCLUDE_INTERNAL section of nsCSSPropList.h.
 #define CSS_PROPERTY_INTERNAL                     (1<<28)
 
+// This property has values that can establish a containing block for
+// fixed positioned and absolutely positioned elements.
+// This should be set for any properties that can cause an element to be
+// such a containing block, as implemented in
+// nsStyleDisplay::IsFixedPosContainingBlock.
+#define CSS_PROPERTY_FIXPOS_CB                    (1<<29)
+
 /**
  * Types of animatable values.
  */

layout/style/nsStyleStructInlines.h

@@ -138,6 +138,8 @@ nsStyleDisplay::HasTransform(const nsIFrame* aContextFrame) const
 bool
 nsStyleDisplay::IsFixedPosContainingBlock(const nsIFrame* aContextFrame) const
 {
+  // NOTE: Any CSS properties that influence the output of this function
+  // should have the CSS_PROPERTY_FIXPOS_CB set on them.
   NS_ASSERTION(aContextFrame->StyleDisplay() == this,
                "unexpected aContextFrame");
   return (IsContainPaint() || HasTransform(aContextFrame) ||