Conditionally create PaintLayer's scrollable area object

third_party/WebKit/Source/core/layout/LayoutBox.cpp

Index: third_party/WebKit/Source/core/layout/LayoutBox.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBox.cpp b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
index 3bc1709ebb82d41630deda811a4c8265d7b1c927..7203d3d9ded29f0c4627fae5de9abcb948962546 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBox.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
@@ -255,14 +255,16 @@ void LayoutBox::styleDidChange(StyleDifference diff, const ComputedStyle* oldSty
 
     // If our zoom factor changes and we have a defined scrollLeft/Top, we need to adjust that value into the
     // new zoomed coordinate space.
-    if (hasOverflowClip() && oldStyle && oldStyle->effectiveZoom() != newStyle.effectiveZoom() && layer()) {
-        if (int left = layer()->scrollableArea()->scrollXOffset()) {
+    if (hasOverflowClip() && oldStyle && oldStyle->effectiveZoom() != newStyle.effectiveZoom()) {
+        PaintLayerScrollableArea* scrollableArea = this->scrollableArea();
+        ASSERT(scrollableArea);
+        if (int left = scrollableArea->scrollXOffset()) {
             left = (left / oldStyle->effectiveZoom()) * newStyle.effectiveZoom();
-            layer()->scrollableArea()->scrollToXOffset(left);
+            scrollableArea->scrollToXOffset(left);
         }
-        if (int top = layer()->scrollableArea()->scrollYOffset()) {
+        if (int top = scrollableArea->scrollYOffset()) {
             top = (top / oldStyle->effectiveZoom()) * newStyle.effectiveZoom();
-            layer()->scrollableArea()->scrollToYOffset(top);
+            scrollableArea->scrollToYOffset(top);
         }
     }
 
@@ -376,31 +378,7 @@ void LayoutBox::updateFromStyle()
     LayoutBoxModelObject::updateFromStyle();
 
     const ComputedStyle& styleToUse = styleRef();
-    bool isViewObject = isLayoutView();
-    bool rootLayerScrolls = document().settings() && document().settings()->rootLayerScrolls();
-
-    // LayoutView of the main frame is resposible from painting base background.
-    if (isViewObject && !document().ownerElement())
-        setHasBoxDecorationBackground(true);

[Xianzhu, 2016/02/26 20:12:57]

BTW the above three lines are moved into LayoutView::updateFromStyle().

-
     setFloating(!isOutOfFlowPositioned() && styleToUse.isFloating());
-
-    bool boxHasOverflowClip = false;
-    if (!styleToUse.isOverflowVisible() && isLayoutBlock() && (rootLayerScrolls || !isViewObject)) {
-        // If overflow has been propagated to the viewport, it has no effect here.
-        if (node() != document().viewportDefiningElement())
-            boxHasOverflowClip = true;
-    }
-
-    if (boxHasOverflowClip != hasOverflowClip()) {
-        // FIXME: This shouldn't be required if we tracked the visual overflow
-        // generated by positioned children or self painting layers. crbug.com/345403
-        for (LayoutObject* child = slowFirstChild(); child; child = child->nextSibling())
-            child->setMayNeedPaintInvalidation();
-    }
-
-    setHasOverflowClip(boxHasOverflowClip);
-
     setHasTransformRelatedProperty(styleToUse.hasTransformRelatedProperty());
     setHasReflection(styleToUse.boxReflect());
 }
@@ -461,7 +439,7 @@ int LayoutBox::pixelSnappedOffsetHeight() const
 LayoutUnit LayoutBox::scrollWidth() const
 {
     if (hasOverflowClip())
-        return layer()->scrollableArea()->scrollWidth();
+        return scrollableArea()->scrollWidth();
     // For objects with visible overflow, this matches IE.
     // FIXME: Need to work right with writing modes.
     if (style()->isLeftToRightDirection())
@@ -472,7 +450,7 @@ LayoutUnit LayoutBox::scrollWidth() const
 LayoutUnit LayoutBox::scrollHeight() const
 {
     if (hasOverflowClip())
-        return layer()->scrollableArea()->scrollHeight();
+        return scrollableArea()->scrollHeight();
     // For objects with visible overflow, this matches IE.
     // FIXME: Need to work right with writing modes.
     return std::max(clientHeight(), layoutOverflowRect().maxY() - borderTop());
@@ -480,12 +458,12 @@ LayoutUnit LayoutBox::scrollHeight() const
 
 LayoutUnit LayoutBox::scrollLeft() const
 {
-    return hasOverflowClip() ? LayoutUnit(layer()->scrollableArea()->scrollXOffset()) : LayoutUnit();
+    return hasOverflowClip() ? LayoutUnit(scrollableArea()->scrollXOffset()) : LayoutUnit();
 }
 
 LayoutUnit LayoutBox::scrollTop() const
 {
-    return hasOverflowClip() ? LayoutUnit(layer()->scrollableArea()->scrollYOffset()) : LayoutUnit();
+    return hasOverflowClip() ? LayoutUnit(scrollableArea()->scrollYOffset()) : LayoutUnit();
 }
 
 int LayoutBox::pixelSnappedScrollWidth() const
@@ -496,7 +474,7 @@ int LayoutBox::pixelSnappedScrollWidth() const
 int LayoutBox::pixelSnappedScrollHeight() const
 {
     if (hasOverflowClip())
-        return snapSizeToPixel(layer()->scrollableArea()->scrollHeight(), location().y() + clientTop());
+        return snapSizeToPixel(scrollableArea()->scrollHeight(), location().y() + clientTop());
     // For objects with visible overflow, this matches IE.
     // FIXME: Need to work right with writing modes.
     return snapSizeToPixel(scrollHeight(), location().y() + clientTop());
@@ -509,7 +487,7 @@ void LayoutBox::setScrollLeft(LayoutUnit newLeft)
     DisableCompositingQueryAsserts disabler;
 
     if (hasOverflowClip())
-        layer()->scrollableArea()->scrollToXOffset(newLeft, ScrollOffsetClamped, ScrollBehaviorAuto);
+        scrollableArea()->scrollToXOffset(newLeft, ScrollOffsetClamped, ScrollBehaviorAuto);
 }
 
 void LayoutBox::setScrollTop(LayoutUnit newTop)
@@ -518,7 +496,7 @@ void LayoutBox::setScrollTop(LayoutUnit newTop)
     DisableCompositingQueryAsserts disabler;
 
     if (hasOverflowClip())
-        layer()->scrollableArea()->scrollToYOffset(newTop, ScrollOffsetClamped, ScrollBehaviorAuto);
+        scrollableArea()->scrollToYOffset(newTop, ScrollOffsetClamped, ScrollBehaviorAuto);
 }
 
 void LayoutBox::scrollToOffset(const DoubleSize& offset, ScrollBehavior scrollBehavior)
@@ -528,7 +506,7 @@ void LayoutBox::scrollToOffset(const DoubleSize& offset, ScrollBehavior scrollBe
     DisableCompositingQueryAsserts disabler;
 
     if (hasOverflowClip())
-        layer()->scrollableArea()->scrollToOffset(offset, ScrollOffsetClamped, scrollBehavior);
+        scrollableArea()->scrollToOffset(offset, ScrollOffsetClamped, scrollBehavior);
 }
 
 // Returns true iff we are attempting an autoscroll inside an iframe with scrolling="no".
@@ -562,7 +540,7 @@ void LayoutBox::scrollRectToVisible(const LayoutRect& rect, const ScrollAlignmen
     if (hasOverflowClip() && !restrictedByLineClamp) {
         // Don't scroll to reveal an overflow layer that is restricted by the -webkit-line-clamp property.
         // This will prevent us from revealing text hidden by the slider in Safari RSS.
-        newRect = layer()->scrollableArea()->scrollIntoView(rect, alignX, alignY, scrollType);
+        newRect = scrollableArea()->scrollIntoView(rect, alignX, alignY, scrollType);
     } else if (!parentBox && canBeProgramaticallyScrolled()) {
         if (FrameView* frameView = this->frameView()) {
             HTMLFrameOwnerElement* ownerElement = document().ownerElement();
@@ -759,7 +737,7 @@ int LayoutBox::verticalScrollbarWidth() const
     if (!hasOverflowClip() || style()->overflowY() == OOVERLAY)
         return 0;
 
-    return layer()->scrollableArea()->verticalScrollbarWidth();
+    return scrollableArea()->verticalScrollbarWidth();
 }
 
 int LayoutBox::horizontalScrollbarHeight() const
@@ -767,7 +745,7 @@ int LayoutBox::horizontalScrollbarHeight() const
     if (!hasOverflowClip() || style()->overflowX() == OOVERLAY)
         return 0;
 
-    return layer()->scrollableArea()->horizontalScrollbarHeight();
+    return scrollableArea()->horizontalScrollbarHeight();
 }
 
 int LayoutBox::intrinsicScrollbarLogicalWidth() const
@@ -775,16 +753,16 @@ int LayoutBox::intrinsicScrollbarLogicalWidth() const
     if (!hasOverflowClip())
         return 0;
 
+    ASSERT(scrollableArea());
+
     if (isHorizontalWritingMode() && style()->overflowY() == OSCROLL) {
-        ASSERT(layer()->scrollableArea());
         // Even with OSCROLL, the scrollbar may not exist (crbug.com/415031).
-        return layer()->scrollableArea()->hasVerticalScrollbar() ? verticalScrollbarWidth() : 0;
+        return scrollableArea()->hasVerticalScrollbar() ? verticalScrollbarWidth() : 0;
     }
 
     if (!isHorizontalWritingMode() && style()->overflowX() == OSCROLL) {
-        ASSERT(layer()->scrollableArea());
         // Even with OSCROLL, the scrollbar may not exist (crbug.com/415031).
-        return layer()->scrollableArea()->hasHorizontalScrollbar() ? horizontalScrollbarHeight() : 0;
+        return scrollableArea()->hasHorizontalScrollbar() ? horizontalScrollbarHeight() : 0;
     }
 
     return 0;
@@ -795,10 +773,10 @@ ScrollResultOneDimensional LayoutBox::scroll(ScrollDirectionPhysical direction,
     // Presumably the same issue as in setScrollTop. See crbug.com/343132.
     DisableCompositingQueryAsserts disabler;
 
-    if (!layer() || !layer()->scrollableArea())
+    if (!scrollableArea())
         return ScrollResultOneDimensional(false);
 
-    return layer()->scrollableArea()->userScroll(direction, granularity, delta);
+    return scrollableArea()->userScroll(direction, granularity, delta);
 }
 
 bool LayoutBox::canBeScrolledAndHasScrollableArea() const
@@ -942,11 +920,14 @@ void LayoutBox::scrollByRecursively(const DoubleSize& delta, ScrollOffsetClampin
         restrictedByLineClamp = !parent()->style()->lineClamp().isNone();
 
     if (hasOverflowClip() && !restrictedByLineClamp) {
-        DoubleSize newScrollOffset = layer()->scrollableArea()->adjustedScrollOffset() + delta;
-        layer()->scrollableArea()->scrollToOffset(newScrollOffset, clamp);
+        PaintLayerScrollableArea* scrollableArea = this->scrollableArea();
+        ASSERT(scrollableArea);
+
+        DoubleSize newScrollOffset = scrollableArea->adjustedScrollOffset() + delta;
+        scrollableArea->scrollToOffset(newScrollOffset, clamp);
 
         // If this layer can't do the scroll we ask the next layer up that can scroll to try
-        DoubleSize remainingScrollOffset = newScrollOffset - layer()->scrollableArea()->adjustedScrollOffset();
+        DoubleSize remainingScrollOffset = newScrollOffset - scrollableArea->adjustedScrollOffset();
         if (!remainingScrollOffset.isZero() && parent()) {
             if (LayoutBox* scrollableBox = enclosingScrollableBox())
                 scrollableBox->scrollByRecursively(remainingScrollOffset, clamp);
@@ -976,7 +957,7 @@ IntSize LayoutBox::scrolledContentOffset() const
     ASSERT(hasOverflowClip());
     ASSERT(hasLayer());
     // FIXME: Return DoubleSize here. crbug.com/414283.
-    return flooredIntSize(layer()->scrollableArea()->scrollOffset());
+    return flooredIntSize(scrollableArea()->scrollOffset());
 }
 
 void LayoutBox::mapScrollingContentsRectToBoxSpace(LayoutRect& rect) const
@@ -1562,9 +1543,11 @@ LayoutRect LayoutBox::overflowClipRect(const LayoutPoint& location, OverlayScrol
 
 void LayoutBox::excludeScrollbars(LayoutRect& rect, OverlayScrollbarSizeRelevancy relevancy) const
 {
-    if (shouldPlaceBlockDirectionScrollbarOnLogicalLeft())
-        rect.move(layer()->scrollableArea()->verticalScrollbarWidth(relevancy), 0);
-    rect.contract(layer()->scrollableArea()->verticalScrollbarWidth(relevancy), layer()->scrollableArea()->horizontalScrollbarHeight(relevancy));
+    if (PaintLayerScrollableArea* scrollableArea = this->scrollableArea()) {
+        if (shouldPlaceBlockDirectionScrollbarOnLogicalLeft())
+            rect.move(scrollableArea->verticalScrollbarWidth(relevancy), 0);
+        rect.contract(scrollableArea->verticalScrollbarWidth(relevancy), scrollableArea->horizontalScrollbarHeight(relevancy));
+    }
 }
 
 LayoutRect LayoutBox::clipRect(const LayoutPoint& location) const
@@ -3761,13 +3744,11 @@ bool LayoutBox::avoidsFloats() const
 
 bool LayoutBox::hasNonCompositedScrollbars() const
 {
-    if (PaintLayer* layer = this->layer()) {
-        if (PaintLayerScrollableArea* scrollableArea = layer->scrollableArea()) {
-            if (scrollableArea->hasHorizontalScrollbar() && !scrollableArea->layerForHorizontalScrollbar())
-                return true;
-            if (scrollableArea->hasVerticalScrollbar() && !scrollableArea->layerForVerticalScrollbar())
-                return true;
-        }
+    if (PaintLayerScrollableArea* scrollableArea = this->scrollableArea()) {
+        if (scrollableArea->hasHorizontalScrollbar() && !scrollableArea->layerForHorizontalScrollbar())
+            return true;
+        if (scrollableArea->hasVerticalScrollbar() && !scrollableArea->layerForVerticalScrollbar())
+            return true;
     }
     return false;
 }