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 01825db216bfcbc45fe7b06d16d95043328839c5..9d316abcb2b3a3f2bb92620d00c487f8a7c08932 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
@@ -805,7 +805,10 @@ void PaintLayer::updateLayerPosition() {
     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());
+    if (newSize != m_size && m_scrollableArea)
+      m_scrollableArea->visibleContentResized();

[dtapuska, 2016/11/02 16:53:21]

I fear you have a re-entry problem here. You are notifying an observer in the
middle of what should be an atomic operation.

Can we call visibleContentResized() after we've assigned m_size ? Or perhaps
even better at the bottom of this method?

[bokan, 2016/11/02 22:41:57]

Good catch, I'll add it to the bottom.

+    m_size = newSize;
     localPoint.moveBy(box->topLeftLocation());
   }