RenderLayerScrollableArea::updateScrollCornerStyle shouldn't do work if we're...

RenderLayerScrollableArea::updateScrollCornerStyle shouldn't do work if we're using overlay scrollbars

This function showed up on a profile of updateStyle in Silk's toggle_drawer
test case, but there no reason to update the scroll corner style if we're using
overlay scrollbars. If the author has created a custom scrollbar, we'll realize
that we don't have overlay scrollbars.

R=esprehn@chromium.org
BUG=335703

Review URL: https://codereview.chromium.org/178903004

git-svn-id: svn://svn.chromium.org/blink/trunk@168601 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/rendering/RenderLayerScrollableArea.cpp

@@ -601,6 +601,9 @@ void RenderLayerScrollableArea::updateAfterLayout()
         if (m_box->hasAutoVerticalScrollbar())
             setHasVerticalScrollbar(hasVerticalOverflow);
 
+        if (hasVerticalOverflow || hasHorizontalOverflow)
+            updateScrollCornerStyle();
+
         layer()->updateSelfPaintingLayer();
 
         // Force an update since we know the scrollbars have changed things.
@@ -958,6 +961,11 @@ bool RenderLayerScrollableArea::scrollsOverflow() const
 
 void RenderLayerScrollableArea::updateScrollCornerStyle()
 {
+    if (!m_scrollCorner && !hasScrollbar())
+        return;
+    if (!m_scrollCorner && hasOverlayScrollbars())
+        return;
+
     RenderObject* actualRenderer = rendererForScrollbar(m_box);
     RefPtr<RenderStyle> corner = m_box->hasOverflowClip() ? actualRenderer->getUncachedPseudoStyle(PseudoStyleRequest(SCROLLBAR_CORNER), actualRenderer->style()) : PassRefPtr<RenderStyle>(nullptr);
     if (corner) {

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

@@ -319,22 +319,25 @@ void ScrollableArea::contentsResized()
 
 bool ScrollableArea::hasOverlayScrollbars() const
 {
-    return (verticalScrollbar() && verticalScrollbar()->isOverlayScrollbar())
-        || (horizontalScrollbar() && horizontalScrollbar()->isOverlayScrollbar());
+    Scrollbar* vScrollbar = verticalScrollbar();
+    if (vScrollbar && vScrollbar->isOverlayScrollbar())
+        return true;
+    Scrollbar* hScrollbar = horizontalScrollbar();
+    return hScrollbar && hScrollbar->isOverlayScrollbar();
 }
 
 void ScrollableArea::setScrollbarOverlayStyle(ScrollbarOverlayStyle overlayStyle)
 {
     m_scrollbarOverlayStyle = overlayStyle;
 
-    if (horizontalScrollbar()) {
-        ScrollbarTheme::theme()->updateScrollbarOverlayStyle(horizontalScrollbar());
-        horizontalScrollbar()->invalidate();
+    if (Scrollbar* scrollbar = horizontalScrollbar()) {
+        ScrollbarTheme::theme()->updateScrollbarOverlayStyle(scrollbar);
+        scrollbar->invalidate();
     }
 
-    if (verticalScrollbar()) {
-        ScrollbarTheme::theme()->updateScrollbarOverlayStyle(verticalScrollbar());
-        verticalScrollbar()->invalidate();
+    if (Scrollbar* scrollbar = verticalScrollbar()) {
+        ScrollbarTheme::theme()->updateScrollbarOverlayStyle(scrollbar);
+        scrollbar->invalidate();
     }
 }