Fix overlay scroll bar color on elements with dark background

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

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@gmail.com>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 821 matching lines @@
 
     // FIXME: Need to detect a swap from custom to native scrollbars (and vice versa).
     if (horizontalScrollbar())
         horizontalScrollbar()->styleChanged();
     if (verticalScrollbar())
         verticalScrollbar()->styleChanged();
 
     updateScrollCornerStyle();
     updateResizerAreaSet();
     updateResizerStyle();
+
+    // Whenever background changes on the scrollable element, the scroll bar
+    // overlay style might need to be changed to have contrast against the
+    // background.
+    Color oldBackground;
+    if (oldStyle) {
+        oldBackground = oldStyle->visitedDependentColor(CSSPropertyBackgroundColor);
+    }
+    Color newBackground = box().style()->visitedDependentColor(CSSPropertyBackgroundColor);
+
+    if (newBackground != oldBackground) {
+        recalculateScrollbarOverlayStyle(newBackground);
+    }
 }
 
 bool PaintLayerScrollableArea::updateAfterCompositingChange()
 {
     layer()->updateScrollingStateAfterCompositingChange();
     const bool layersChanged = m_topmostScrollChild != m_nextTopmostScrollChild;
     m_topmostScrollChild = m_nextTopmostScrollChild;
     m_nextTopmostScrollChild = nullptr;
     return layersChanged;
 }
@@ skipping 102 matching lines @@
 
         if (ShadowRoot* shadowRoot = node->containingShadowRoot()) {
             if (shadowRoot->type() == ShadowRootType::UserAgent)
                 return *shadowRoot->host()->layoutObject();
         }
     }
 
     return layoutObject;
 }
 
+bool PaintLayerScrollableArea::useCustomScrollbarStyle() const
+{
+    const LayoutObject& actualLayoutObject = layoutObjectForScrollbar(box());
+    return actualLayoutObject.isBox() && actualLayoutObject.styleRef().hasPseudoStyle(SCROLLBAR);
+}
+
 bool PaintLayerScrollableArea::needsScrollbarReconstruction() const
 {
     const LayoutObject& actualLayoutObject = layoutObjectForScrollbar(box());
-    bool shouldUseCustom = actualLayoutObject.isBox() && actualLayoutObject.styleRef().hasPseudoStyle(SCROLLBAR);
+    bool shouldUseCustom = useCustomScrollbarStyle();
     bool hasAnyScrollbar = hasScrollbar();
     bool hasCustom = (hasHorizontalScrollbar() && horizontalScrollbar()->isCustomScrollbar()) || (hasVerticalScrollbar() && verticalScrollbar()->isCustomScrollbar());
     bool didCustomScrollbarOwnerChanged = false;
 
     if (hasHorizontalScrollbar() && horizontalScrollbar()->isCustomScrollbar()) {
         if (actualLayoutObject != toLayoutScrollbar(horizontalScrollbar())->owningLayoutObject())
             didCustomScrollbarOwnerChanged = true;
     }
 
     if (hasVerticalScrollbar() && verticalScrollbar()->isCustomScrollbar()) {
         if (actualLayoutObject != toLayoutScrollbar(verticalScrollbar())->owningLayoutObject())
             didCustomScrollbarOwnerChanged = true;
     }
 
     return hasAnyScrollbar && ((shouldUseCustom != hasCustom) || (shouldUseCustom && didCustomScrollbarOwnerChanged));
 }
 
 void PaintLayerScrollableArea::setHasHorizontalScrollbar(bool hasScrollbar)
 {
     if (hasScrollbar == hasHorizontalScrollbar())
         return;
 
     setScrollbarNeedsPaintInvalidation(HorizontalScrollbar);
 
-    m_scrollbarManager.setHasHorizontalScrollbar(hasScrollbar);
+    m_scrollbarManager.setHasHorizontalScrollbar(hasScrollbar, useCustomScrollbarStyle());
 
     // Destroying or creating one bar can cause our scrollbar corner to come and go. We need to update the opposite scrollbar's style.
     if (hasHorizontalScrollbar())
         horizontalScrollbar()->styleChanged();
     if (hasVerticalScrollbar())
         verticalScrollbar()->styleChanged();
 
     setScrollCornerNeedsPaintInvalidation();
 
     // Force an update since we know the scrollbars have changed things.
     if (box().document().hasAnnotatedRegions())
         box().document().setAnnotatedRegionsDirty(true);
 }
 
 void PaintLayerScrollableArea::setHasVerticalScrollbar(bool hasScrollbar)
 {
     if (hasScrollbar == hasVerticalScrollbar())
         return;
 
     setScrollbarNeedsPaintInvalidation(VerticalScrollbar);
 
-    m_scrollbarManager.setHasVerticalScrollbar(hasScrollbar);
+    m_scrollbarManager.setHasVerticalScrollbar(hasScrollbar, useCustomScrollbarStyle());
 
     // Destroying or creating one bar can cause our scrollbar corner to come and go. We need to update the opposite scrollbar's style.
     if (hasHorizontalScrollbar())
         horizontalScrollbar()->styleChanged();
     if (hasVerticalScrollbar())
         verticalScrollbar()->styleChanged();
 
     setScrollCornerNeedsPaintInvalidation();
 
     // Force an update since we know the scrollbars have changed things.
@@ skipping 443 matching lines @@
     ASSERT(!m_vBarIsAttached || m_vBar);
     m_canDetachScrollbars = detach ? 1 : 0;
     if (!detach) {
         if (m_hBar && !m_hBarIsAttached)
             destroyScrollbar(HorizontalScrollbar);
         if (m_vBar && !m_vBarIsAttached)
             destroyScrollbar(VerticalScrollbar);
     }
 }
 
-void PaintLayerScrollableArea::ScrollbarManager::setHasHorizontalScrollbar(bool hasScrollbar)
+void PaintLayerScrollableArea::ScrollbarManager::setHasHorizontalScrollbar(bool hasScrollbar, bool useCustomScrollbarStyle)
 {
     if (hasScrollbar) {
         // This doesn't hit in any tests, but since the equivalent code in setHasVerticalScrollbar
         // does, presumably this code does as well.
         DisableCompositingQueryAsserts disabler;
-        if (!m_hBar)
-            m_hBar = createScrollbar(HorizontalScrollbar);
-        m_hBarIsAttached = 1;
+        if (!m_hBar) {
+            m_hBar = createScrollbar(HorizontalScrollbar, useCustomScrollbarStyle);
+            m_hBarIsAttached = 1;
+            if (!useCustomScrollbarStyle)
+                m_scrollableArea->didAddScrollbar(*m_hBar, HorizontalScrollbar);

[Xianzhu, 2016/03/02 00:03:50]

I suggest to check the condition in ScrollableArea::didAddScrollbar() because
the function doesn't explicitly disallow custom scrollbars based on its name.

In ScrollbarArea::didAddScrollbar() you can add:

  if (scrollbar.isCustomScrollbar())
     return;

+        } else {
+            m_hBarIsAttached = 1;
+        }
+
     } else {
         m_hBarIsAttached = 0;
         if (!m_canDetachScrollbars)
             destroyScrollbar(HorizontalScrollbar);
     }
 }
 
-void PaintLayerScrollableArea::ScrollbarManager::setHasVerticalScrollbar(bool hasScrollbar)
+void PaintLayerScrollableArea::ScrollbarManager::setHasVerticalScrollbar(bool hasScrollbar, bool useCustomScrollbarStyle)
 {
     if (hasScrollbar) {
         DisableCompositingQueryAsserts disabler;
-        if (!m_vBar)
-            m_vBar = createScrollbar(VerticalScrollbar);
-        m_vBarIsAttached = 1;
+        if (!m_vBar) {
+            m_vBar = createScrollbar(VerticalScrollbar, useCustomScrollbarStyle);
+            m_vBarIsAttached = 1;
+            if (!useCustomScrollbarStyle)
+                m_scrollableArea->didAddScrollbar(*m_vBar, VerticalScrollbar);
+        } else {
+            m_vBarIsAttached = 1;
+        }
+
     } else {
         m_vBarIsAttached = 0;
         if (!m_canDetachScrollbars)
             destroyScrollbar(VerticalScrollbar);
     }
 }
 
-PassRefPtrWillBeRawPtr<Scrollbar> PaintLayerScrollableArea::ScrollbarManager::createScrollbar(ScrollbarOrientation orientation)
+PassRefPtrWillBeRawPtr<Scrollbar> PaintLayerScrollableArea::ScrollbarManager::createScrollbar(ScrollbarOrientation orientation, bool useCustomScrollbarStyle)

[Xianzhu, 2016/03/02 00:03:50]

I suggest to avoid the new parameter and call useCustomScrollbarStyle() here.
This avoids a bool parameter which is not suggested in our coding style.

 {
     ASSERT(orientation == HorizontalScrollbar ? !m_hBarIsAttached : !m_vBarIsAttached);
     RefPtrWillBeRawPtr<Scrollbar> scrollbar = nullptr;
     const LayoutObject& actualLayoutObject = layoutObjectForScrollbar(m_scrollableArea->box());
-    bool hasCustomScrollbarStyle = actualLayoutObject.isBox() && actualLayoutObject.styleRef().hasPseudoStyle(SCROLLBAR);
-    if (hasCustomScrollbarStyle) {
+    if (useCustomScrollbarStyle) {
         scrollbar = LayoutScrollbar::createCustomScrollbar(m_scrollableArea.get(), orientation, actualLayoutObject.node());
     } else {
         ScrollbarControlSize scrollbarSize = RegularScrollbar;
         if (actualLayoutObject.styleRef().hasAppearance())
             scrollbarSize = LayoutTheme::theme().scrollbarControlSizeForPart(actualLayoutObject.styleRef().appearance());
         scrollbar = Scrollbar::create(m_scrollableArea.get(), orientation, scrollbarSize, &m_scrollableArea->box().frame()->page()->chromeClient());
-        if (orientation == HorizontalScrollbar)
-            m_scrollableArea->didAddScrollbar(*scrollbar, HorizontalScrollbar);
-        else
-            m_scrollableArea->didAddScrollbar(*scrollbar, VerticalScrollbar);
     }
     m_scrollableArea->box().document().view()->addChild(scrollbar.get());
     return scrollbar.release();
 }
 
 void PaintLayerScrollableArea::ScrollbarManager::destroyScrollbar(ScrollbarOrientation orientation)
 {
     RefPtrWillBeMember<Scrollbar>& scrollbar = orientation == HorizontalScrollbar ? m_hBar : m_vBar;
     ASSERT(orientation == HorizontalScrollbar ? !m_hBarIsAttached: !m_vBarIsAttached);
     if (!scrollbar)
@@ skipping 14 matching lines @@
 }
 
 DEFINE_TRACE(PaintLayerScrollableArea::ScrollbarManager)
 {
     visitor->trace(m_scrollableArea);
     visitor->trace(m_hBar);
     visitor->trace(m_vBar);
 }
 
 } // namespace blink