Overlay scrollbars flush with window edge

third_party/WebKit/Source/platform/scroll/Scrollbar.cpp

 /*
  * Copyright (C) 2004, 2006, 2008 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 45 matching lines @@
       m_pressedPos(0),
       m_scrollPos(0),
       m_draggingDocument(false),
       m_documentDragPos(0),
       m_enabled(true),
       m_scrollTimer(scrollableArea->getTimerTaskRunner(),
                     this,
                     &Scrollbar::autoscrollTimerFired),
       m_elasticOverscroll(0),
       m_trackNeedsRepaint(true),
-      m_thumbNeedsRepaint(true) {
+      m_thumbNeedsRepaint(true),
+      m_hitBeginOrEnd(true) {
   m_theme.registerScrollbar(*this);
 
   // FIXME: This is ugly and would not be necessary if we fix cross-platform
   // code to actually query for scrollbar thickness and use it when sizing
   // scrollbars (rather than leaving one dimension of the scrollbar alone when
   // sizing).
   int thickness = m_theme.scrollbarThickness(controlSize);
   m_themeScrollbarThickness = thickness;
   if (m_hostWindow)
     thickness = m_hostWindow->windowToViewportScalar(thickness);
@@ skipping 46 matching lines @@
   ASSERT(m_scrollableArea);
 
   float position = scrollableAreaCurrentPos();
   if (position == m_currentPos)
     return;
 
   float oldPosition = m_currentPos;
   int oldThumbPosition = theme().thumbPosition(*this);
   m_currentPos = position;
 
-  ScrollbarPart invalidParts =
-      theme().invalidateOnThumbPositionChange(*this, oldPosition, position);
+  bool oldHitBeginOrEnd = m_hitBeginOrEnd;
+  int thumbPosition = theme().thumbPosition(*this);
+  m_hitBeginOrEnd =
+      thumbPosition == 0 ||
+      thumbPosition + theme().thumbLength(*this) == theme().trackLength(*this);
+
+  ScrollbarPart invalidParts = theme().invalidateOnThumbPositionChange(
+      *this, oldPosition, position, oldHitBeginOrEnd != m_hitBeginOrEnd);
   setNeedsPaintInvalidation(invalidParts);
 
   if (m_pressedPart == ThumbPart)
     setPressedPos(m_pressedPos + theme().thumbPosition(*this) -
                   oldThumbPosition);
 }
 
 void Scrollbar::disconnectFromScrollableArea() {
   m_scrollableArea = nullptr;
 }
@@ skipping 495 matching lines @@
   if (m_theme.shouldRepaintAllPartsOnInvalidation())
     invalidParts = AllParts;
   if (invalidParts & ~ThumbPart)
     m_trackNeedsRepaint = true;
   if (invalidParts & ThumbPart)
     m_thumbNeedsRepaint = true;
   if (m_scrollableArea)
     m_scrollableArea->setScrollbarNeedsPaintInvalidation(orientation());
 }
 
+bool Scrollbar::hasScrollCorner() const {
+  return m_scrollableArea->hasLayerForScrollCorner();
+}
+
 }  // namespace blink