Change CSS containment should invalidate layout

third_party/WebKit/Source/core/layout/LayoutBlock.cpp

Index: third_party/WebKit/Source/core/layout/LayoutBlock.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBlock.cpp b/third_party/WebKit/Source/core/layout/LayoutBlock.cpp
index 5d467351fbbe677e581143a030b555be27cce364..347a1eca79335624731eb8e5c127da8d4564f447 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBlock.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBlock.cpp
@@ -143,21 +143,26 @@ void LayoutBlock::styleWillChange(StyleDifference diff, const ComputedStyle& new
     setIsAtomicInlineLevel(newStyle.isDisplayInlineType());
 
     if (oldStyle && parent()) {
-        bool oldHasTransformRelatedProperty = oldStyle->hasTransformRelatedProperty();
-        bool newHasTransformRelatedProperty = newStyle.hasTransformRelatedProperty();
-        bool oldStyleIsContainer = oldStyle->position() != StaticPosition || oldHasTransformRelatedProperty;
-
-        if (oldStyleIsContainer && (newStyle.position() == StaticPosition || (oldHasTransformRelatedProperty && !newHasTransformRelatedProperty))) {
+        // Should keep in sync with LayoutObject::canContainFixedPositionObjects().
+        bool oldStyleContainsFixedPosition = oldStyle->hasTransformRelatedProperty() || oldStyle->containsPaint();

[chrishtr, 2016/06/16 04:31:06]

Factor hasTransformRelatedProperty() || oldStyle->containsPaint() into a helper
method, with a style as parameter, used here and in
canContainFixedPositionObjects.

[trchen, 2016/06/16 22:09:52]

Done.

+        bool newStyleContainsFixedPosition = newStyle.hasTransformRelatedProperty() || newStyle.containsPaint();
+        // Should keep in sync with LayoutObject::canContainAbsolutePositionObjects().
+        bool oldStyleContainsAbsolutePosition = oldStyle->position() != StaticPosition || oldStyleContainsFixedPosition;

[chrishtr, 2016/06/16 04:31:06]

Same here.

[trchen, 2016/06/16 22:09:52]

Done.

+        bool newStyleContainsAbsolutePosition = newStyle.position() != StaticPosition || newStyleContainsFixedPosition;
+
+        if ((oldStyleContainsFixedPosition && !newStyleContainsFixedPosition)
+            || (oldStyleContainsAbsolutePosition && !newStyleContainsAbsolutePosition)) {
             // Clear our positioned objects list. Our absolute and fixed positioned descendants will be
             // inserted into our containing block's positioned objects list during layout.
             removePositionedObjects(nullptr, NewContainingBlock);
-        } else if (!oldStyleIsContainer && (newStyle.position() != StaticPosition || newHasTransformRelatedProperty)) {
+        }
+        if (!oldStyleContainsAbsolutePosition && newStyleContainsAbsolutePosition) {
             // Remove our absolutely positioned descendants from their current containing block.
             // They will be inserted into our positioned objects list during layout.
             if (LayoutBlock* cb = containingBlockForAbsolutePosition())
                 cb->removePositionedObjects(this, NewContainingBlock);
         }
-        if (!oldHasTransformRelatedProperty && newHasTransformRelatedProperty) {
+        if (!oldStyleContainsFixedPosition && newStyleContainsFixedPosition) {
             // Remove our fixed positioned descendants from their current containing block.
             // They will be inserted into our positioned objects list during layout.
             if (LayoutBlock* cb = containerForFixedPosition())
@@ -192,9 +197,11 @@ void LayoutBlock::styleDidChange(StyleDifference diff, const ComputedStyle* oldS
 
     if (oldStyle && parent()) {
         if (oldStyle->position() != newStyle.position() && newStyle.position() != StaticPosition) {
-            // Remove our absolute and fixed positioned descendants from their new containing block,
-            // in case containingBlock() changes by the change to the position property.
-            // See styleWillChange() for other cases.
+            // In LayoutObject::styleWillChange() we already removed ourself from our old containg

[chrishtr, 2016/06/16 04:31:06]

Typo: "containg"

[trchen, 2016/06/16 22:09:52]

Done.

+            // block's positioned descendant list, and we will be inserted to the new containing
+            // block's list during layout. However the positioned descendant layout logic assumes
+            // layout objects to obey parent-child order in the list. Remove our descendants here
+            // so they will be re-inserted after us.
             if (LayoutBlock* cb = containingBlock())
                 cb->removePositionedObjects(this, NewContainingBlock);
         }