Clip scrollbars to box bounds when they don't fit.

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

Index: third_party/WebKit/Source/core/paint/BoxClipper.cpp
diff --git a/third_party/WebKit/Source/core/paint/BoxClipper.cpp b/third_party/WebKit/Source/core/paint/BoxClipper.cpp
index 6355078338ba7f8605031ba53decf96cabb74ae5..19c86d7ea712dbe9bbe0e6a7330205a0b987f8d0 100644
--- a/third_party/WebKit/Source/core/paint/BoxClipper.cpp
+++ b/third_party/WebKit/Source/core/paint/BoxClipper.cpp
@@ -20,19 +20,34 @@ BoxClipper::BoxClipper(const LayoutBox& box, const PaintInfo& paintInfo, const L
     , m_paintInfo(paintInfo)
     , m_clipType(DisplayItem::UninitializedType)
 {
-    if (m_paintInfo.phase == PaintPhaseBlockBackground || m_paintInfo.phase == PaintPhaseSelfOutline || m_paintInfo.phase == PaintPhaseMask)
+    if ((m_paintInfo.phase == PaintPhaseBlockBackground && contentsClipBehavior != ClipForScrollbars)
+        || m_paintInfo.phase == PaintPhaseSelfOutline || m_paintInfo.phase == PaintPhaseMask)
         return;
 
-    bool isControlClip = m_box.hasControlClip();
-    bool isOverflowClip = m_box.hasOverflowClip() && !m_box.layer()->isSelfPaintingLayer();
+    bool hasControlClip = m_box.hasControlClip();
+    bool hasOverflowClip = m_box.hasOverflowClip() && !m_box.layer()->isSelfPaintingLayer();
 
-    if (!isControlClip && !isOverflowClip)
+    if (!hasControlClip && !hasOverflowClip)
         return;
 
-    LayoutRect clipRect = isControlClip ? m_box.controlClipRect(accumulatedOffset) : m_box.overflowClipRect(accumulatedOffset);
+    LayoutRect clipRect;
+
+    if (hasControlClip) {
+        clipRect = m_box.controlClipRect(accumulatedOffset);
+    } else {
+        ASSERT(hasOverflowClip);
+        if (contentsClipBehavior == ClipForScrollbars) {
+            clipRect = m_box.borderBoxRect();
+            clipRect.moveBy(accumulatedOffset);
+        } else {
+            clipRect = m_box.overflowClipRect(accumulatedOffset);
+        }
+    }
+
     FloatRoundedRect clipRoundedRect(0, 0, 0, 0);
-    bool hasBorderRadius = m_box.style()->hasBorderRadius();
-    if (hasBorderRadius)
+    // Scrollbars paint on top of a rounded border.
+    bool shouldClipBorderRadius = m_box.style()->hasBorderRadius() && contentsClipBehavior != ClipForScrollbars;
+    if (shouldClipBorderRadius)
         clipRoundedRect = m_box.style()->getRoundedInnerBorderFor(LayoutRect(accumulatedOffset, m_box.size()));
 
     if (contentsClipBehavior == SkipContentsClipIfPossible) {
@@ -41,7 +56,7 @@ BoxClipper::BoxClipper(const LayoutBox& box, const PaintInfo& paintInfo, const L
             return;
 
         LayoutRect conservativeClipRect = clipRect;
-        if (hasBorderRadius)
+        if (shouldClipBorderRadius)
             conservativeClipRect.intersect(LayoutRect(clipRoundedRect.radiusCenterRect()));
         conservativeClipRect.moveBy(-accumulatedOffset);
         if (m_box.hasLayer())
@@ -53,7 +68,7 @@ BoxClipper::BoxClipper(const LayoutBox& box, const PaintInfo& paintInfo, const L
     if (!m_paintInfo.context->paintController().displayItemConstructionIsDisabled()) {
         m_clipType = m_paintInfo.displayItemTypeForClipping();
         Vector<FloatRoundedRect> roundedRects;
-        if (hasBorderRadius)
+        if (shouldClipBorderRadius)
             roundedRects.append(clipRoundedRect);
         m_paintInfo.context->paintController().createAndAppend<ClipDisplayItem>(m_box, m_clipType, pixelSnappedIntRect(clipRect), roundedRects);
     }