Implement overlay scrollbar fade out for non-composited scrollers.

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

Index: third_party/WebKit/Source/core/paint/PaintLayer.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.cpp b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
index e89f69a809021bf015f878445a7b1595d3c7fee5..f782b1f5fccd6c254b4cc187356ca2afcaa1efb1 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
@@ -793,12 +793,15 @@ bool PaintLayer::update3DTransformedDescendantStatus() {
 void PaintLayer::updateLayerPosition() {
   LayoutPoint localPoint;
 
+  bool didResize = false;
   if (layoutObject()->isInline() && layoutObject()->isLayoutInline()) {
     LayoutInline* inlineFlow = toLayoutInline(layoutObject());
     IntRect lineBox = enclosingIntRect(inlineFlow->linesBoundingBox());
     m_size = lineBox.size();
   } else if (LayoutBox* box = layoutBox()) {
-    m_size = pixelSnappedIntSize(box->size(), box->location());
+    IntSize newSize = pixelSnappedIntSize(box->size(), box->location());
+    didResize = newSize != m_size;
+    m_size = newSize;
     localPoint.moveBy(box->topLeftLocation());
   }
 
@@ -856,6 +859,9 @@ void PaintLayer::updateLayerPosition() {
 
   m_location = localPoint;
 
+  if (m_scrollableArea && didResize)
+    m_scrollableArea->visibleSizeChanged();
+
 #if DCHECK_IS_ON()
   m_needsPositionUpdate = false;
 #endif