Overlay scrollbars flush with window edge

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

 /*
  * Copyright (C) 2011 Google 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
@@ skipping 47 matching lines @@
       m_allowHitTest(allowHitTest),
       m_useSolidColor(false) {}
 
 bool ScrollbarThemeOverlay::shouldRepaintAllPartsOnInvalidation() const {
   return false;
 }
 
 ScrollbarPart ScrollbarThemeOverlay::invalidateOnThumbPositionChange(
     const ScrollbarThemeClient&,
     float oldPosition,
-    float newPosition) const {
+    float newPosition,
+    bool hitBeginOrEndChanged) const {
+  if (hitBeginOrEndChanged)
+    return ThumbPart;
   return NoPart;
 }
 
 ScrollbarPart ScrollbarThemeOverlay::invalidateOnEnabledChange() const {
   return NoPart;
 }
 
 int ScrollbarThemeOverlay::scrollbarThickness(
     ScrollbarControlSize controlSize) {
   return m_thumbThickness + m_scrollbarMargin;
@@ skipping 118 matching lines @@
   WebCanvas* canvas = context.canvas();
 
   WebThemeEngine::Part part = WebThemeEngine::PartScrollbarHorizontalThumb;
   if (scrollbar.orientation() == VerticalScrollbar)
     part = WebThemeEngine::PartScrollbarVerticalThumb;
 
   blink::WebThemeEngine::ExtraParams params;
   params.scrollbarThumb.scrollbarTheme =
       static_cast<WebScrollbarOverlayColorTheme>(
           scrollbar.getScrollbarOverlayColorTheme());
+  params.scrollbarThumb.isVerticalScrollbar =
+      scrollbar.orientation() == VerticalScrollbar;
+  params.scrollbarThumb.isLeftVerticalScrollbar =
+      scrollbar.isLeftSideVerticalScrollbar();
+
+  int currentThumbPosition = ScrollbarTheme::thumbPosition(scrollbar);
+
+  params.scrollbarThumb.hitStart = currentThumbPosition == 0;
+  params.scrollbarThumb.hitEnd =
+      !scrollbar.hasScrollCorner() &&
+      currentThumbPosition + thumbLength(scrollbar) == trackLength(scrollbar);
 
   Platform::current()->themeEngine()->paint(canvas, part, state, WebRect(rect),
                                             &params);
 }
 
 ScrollbarPart ScrollbarThemeOverlay::hitTest(
     const ScrollbarThemeClient& scrollbar,
     const IntPoint& position) {
   if (m_allowHitTest == DisallowHitTest)
     return NoPart;
@@ skipping 47 matching lines @@
 
   WebThemeEngine::Part part = WebThemeEngine::PartScrollbarHorizontalThumb;
   if (scrollbar.orientation() == VerticalScrollbar)
     part = WebThemeEngine::PartScrollbarVerticalThumb;
 
   DCHECK(Platform::current()->themeEngine());
   return Platform::current()->themeEngine()->ninePatchAperture(part);
 }
 
 }  // namespace blink