Set m_{width,height}AvailableToChildrenChanged when scrollbars appear

third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp

Index: third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
index 656b4effafa988901318f24c2df30272ccbf154b..b79cdb52ae4bc24963782bc7a981484cbaa5a080 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
@@ -682,6 +682,17 @@ bool PaintLayerScrollableArea::updateAfterLayout(SubtreeLayoutScope* delayedLayo
                 m_inOverflowRelayout = true;
                 if (delayedLayoutScope) {
                     delayedLayoutScope->setNeedsLayout(&box(), LayoutInvalidationReason::ScrollbarChanged);
+                    // Since we can't pass true to layoutBlock to force relaying out the children, mark them explicitly.
+                    // They do have to be laid out again because their available width has now changed.
+                    for (LayoutObject* child = box().slowFirstChild(); child; child = child->nextSibling())
+                        delayedLayoutScope->setNeedsLayout(child, LayoutInvalidationReason::ScrollbarChanged);
+                    TrackedLayoutBoxListHashSet* positionedDescendants = box().isLayoutBlock() ? toLayoutBlock(box()).positionedObjects() : 0;

[mstensho (USE GERRIT), 2016/03/17 21:23:36]

0 -> nullptr

+                    if (positionedDescendants) {
+                        for (auto* positionedObject : *positionedDescendants) {
+                            delayedLayoutScope->setNeedsLayout(positionedObject, LayoutInvalidationReason::ScrollbarChanged);
+                        }

[mstensho (USE GERRIT), 2016/03/17 21:23:36]

Superfluous braces.

+                    }
+
                     didMarkForDelayedLayout = true;
                 } else {
                     SubtreeLayoutScope layoutScope(box());