RLSA needsLayout on customscrollbar thickness change.

Source/core/rendering/RenderBlock.cpp

Index: Source/core/rendering/RenderBlock.cpp
diff --git a/Source/core/rendering/RenderBlock.cpp b/Source/core/rendering/RenderBlock.cpp
index 01828a11a386acf151a0fd570b615d77a67acf45..4945e3d1574d1e386c1e135153e8b148389a58b6 100644
--- a/Source/core/rendering/RenderBlock.cpp
+++ b/Source/core/rendering/RenderBlock.cpp
@@ -152,7 +152,7 @@ RenderBlock::RenderBlock(ContainerNode* node)
     , m_hasMarginAfterQuirk(false)
     , m_beingDestroyed(false)
     , m_hasMarkupTruncation(false)
-    , m_hasBorderOrPaddingLogicalWidthChanged(false)
+    , m_widthAvailableToChildrenChanged(false)
     , m_hasOnlySelfCollapsingChildren(false)
     , m_descendantsWithFloatsMarkedForLayout(false)
 {
@@ -367,7 +367,7 @@ void RenderBlock::styleDidChange(StyleDifference diff, const RenderStyle* oldSty
 
     // It's possible for our border/padding to change, but for the overall logical width of the block to
     // end up being the same. We keep track of this change so in layoutBlock, we can know to set relayoutChildren=true.
-    m_hasBorderOrPaddingLogicalWidthChanged = oldStyle && diff.needsFullLayout() && needsLayout() && borderOrPaddingLogicalWidthChanged(oldStyle, newStyle);
+    m_widthAvailableToChildrenChanged |= oldStyle && diff.needsFullLayout() && needsLayout() && borderOrPaddingLogicalWidthChanged(oldStyle, newStyle);
 
     // If the style has unloaded images, want to notify the ResourceLoadPriorityOptimizer so that
     // network priorities can be set.
@@ -1434,8 +1434,8 @@ bool RenderBlock::updateImageLoadingPriorities()
 
 bool RenderBlock::widthAvailableToChildrenHasChanged()
 {
-    bool widthAvailableToChildrenHasChanged = m_hasBorderOrPaddingLogicalWidthChanged;
-    m_hasBorderOrPaddingLogicalWidthChanged = false;
+    bool widthAvailableToChildrenHasChanged = m_widthAvailableToChildrenChanged;
+    m_widthAvailableToChildrenChanged = false;
 
     // If we use border-box sizing, have percentage padding, and our parent has changed width then the width available to our children has changed even
     // though our own width has remained the same.