Fully (?) fix overflow: auto with delayed scroll updates

The scroll delaying code, used by Flexbox, never lays out the
parent after the child relayout. This is a problem especially
because the layout can add/remove a horizontal scrollbar,
which changes the height of the element. A vertical scrollbar
has this problem less often, though it sometimes does, especially
in case of flex items. As far as I can tell, this never worked
correctly since the scroll delaying code existed.

This patch changes it so that when we eventually do the scroll info
updates, we mark the ancestor chain for layout (up to the outer flexbox)
and then call layoutFlexItems again, to do the correct layout.

See also the discussion thread at
https://groups.google.com/a/chromium.org/d/topic/layout-dev/e7Wzvxu7qiA/discussion

BUG=579401,584363

Review URL: https://codereview.chromium.org/1734203002

Cr-Commit-Position: refs/heads/master@{#377826}

third_party/WebKit/LayoutTests/css3/flexbox/overflow-auto-resizes-correctly-expected.txt

@@ -7,8 +7,8 @@ PASS hbox.parentNode.clientHeight is hbox.parentNode.scrollHeight
 PASS hbox.clientHeight is hbox.scrollHeight
 PASS intrinsicHeightBox.clientHeight is intrinsicHeightBox.scrollHeight
 PASS scrollbarSize is not 0
-PASS inner.clientWidth is 100 - scrollbarSize
-PASS inner.offsetWidth is 100
+PASS inner.clientWidth is 100
+PASS inner.offsetWidth is 100 + scrollbarSize
 PASS vbox.clientWidth is 100
 PASS vbox.offsetWidth is 100 + scrollbarSize
 PASS successfullyParsed is true

third_party/WebKit/LayoutTests/css3/flexbox/overflow-auto-resizes-correctly.html

@@ -19,6 +19,7 @@
 }
 .vbox {
   overflow-y: auto;
+  max-height: 200px;
 }
 .intrinsic-height-box {
   min-height: -webkit-min-content;
@@ -76,11 +77,9 @@
   var scrollbarSize = measure.offsetWidth - measure.clientWidth;
   shouldNotBe("scrollbarSize", "0");
 
-  // TODO(cbiesinger): These should really be 100 and 100 + scrollbarSize, but
-  // we currently have a bug that makes it not so.
   var inner = document.getElementById('inner');
-  shouldBe("inner.clientWidth", "100 - scrollbarSize");
-  shouldBe("inner.offsetWidth", "100");
+  shouldBe("inner.clientWidth", "100");
+  shouldBe("inner.offsetWidth", "100 + scrollbarSize");
 
   var vbox = document.querySelector('.vbox');
   shouldBe("vbox.clientWidth", "100");

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

@@ -837,8 +837,10 @@ void LayoutBlock::startDelayUpdateScrollInfo()
     ++gDelayUpdateScrollInfo;
 }
 
-void LayoutBlock::finishDelayUpdateScrollInfo()
+bool LayoutBlock::finishDelayUpdateScrollInfo(SubtreeLayoutScope* layoutScope)
 {
+    bool childrenMarkedForRelayout = false;
+
     --gDelayUpdateScrollInfo;
     ASSERT(gDelayUpdateScrollInfo >= 0);
     if (gDelayUpdateScrollInfo == 0) {
@@ -849,10 +851,11 @@ void LayoutBlock::finishDelayUpdateScrollInfo()
 
         for (auto* block : *infoSet) {
             if (block->hasOverflowClip()) {
-                block->layer()->scrollableArea()->updateAfterLayout();
+                childrenMarkedForRelayout |= block->layer()->scrollableArea()->updateAfterLayout(layoutScope);
             }
         }
     }
+    return childrenMarkedForRelayout;
 }
 
 void LayoutBlock::updateScrollInfoAfterLayout()

third_party/WebKit/Source/core/layout/LayoutBlock.h

@@ -338,8 +338,9 @@ class CORE_EXPORT LayoutBlock : public LayoutBox {
     // descendant. If multiple calls are made to startDelayUpdateScrollInfo(),
     // finishDelayUpdateScrollInfo() will do nothing until finishDelayUpdateScrollInfo()
     // is called the same number of times.
+    // finishDelayUpdateScrollInfo returns true when it marked something for layout.
     static void startDelayUpdateScrollInfo();
-    static void finishDelayUpdateScrollInfo();
+    static bool finishDelayUpdateScrollInfo(SubtreeLayoutScope*);
 
     void updateScrollInfoAfterLayout();
 

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

@@ -532,7 +532,7 @@ void LayoutDeprecatedFlexibleBox::layoutHorizontalBox(bool relayoutChildren)
         }
     } while (haveFlex);
 
-    LayoutBlock::finishDelayUpdateScrollInfo();
+    LayoutBlock::finishDelayUpdateScrollInfo(nullptr);
 
     if (remainingSpace > 0 && ((style()->isLeftToRightDirection() && style()->boxPack() != Start)
         || (!style()->isLeftToRightDirection() && style()->boxPack() != End))) {
@@ -783,7 +783,7 @@ void LayoutDeprecatedFlexibleBox::layoutVerticalBox(bool relayoutChildren)
         }
     } while (haveFlex);
 
-    LayoutBlock::finishDelayUpdateScrollInfo();
+    LayoutBlock::finishDelayUpdateScrollInfo(nullptr);
 
     if (style()->boxPack() != Start && remainingSpace > 0) {
         // Children must be repositioned.

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

@@ -288,7 +288,8 @@ void LayoutFlexibleBox::layoutBlock(bool relayoutChildren)
 
         layoutFlexItems(relayoutChildren, layoutScope);
 
-        LayoutBlock::finishDelayUpdateScrollInfo();
+        if (LayoutBlock::finishDelayUpdateScrollInfo(&layoutScope))
+            layoutFlexItems(false, layoutScope);
 
         if (logicalHeight() != previousHeight)
             relayoutChildren = true;

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

@@ -612,10 +612,12 @@ void PaintLayerScrollableArea::scrollToPosition(const DoublePoint& scrollPositio
         ScrollableArea::setScrollPosition(newScrollPosition, scrollType, scrollBehavior);
 }
 
-void PaintLayerScrollableArea::updateAfterLayout()
+bool PaintLayerScrollableArea::updateAfterLayout(SubtreeLayoutScope* delayedLayoutScope)
 {
     ASSERT(box().hasOverflowClip());
 
+    bool didMarkForDelayedLayout = false;
+
     if (needsScrollbarReconstruction()) {
         m_scrollbarManager.setCanDetachScrollbars(false);
         setHasHorizontalScrollbar(false);
@@ -683,14 +685,19 @@ void PaintLayerScrollableArea::updateAfterLayout()
         if ((horizontalScrollBarChanged && box().style()->overflowX() != OOVERLAY) || (verticalScrollBarChanged && box().style()->overflowY() != OOVERLAY)) {
             if (!m_inOverflowRelayout) {
                 m_inOverflowRelayout = true;
-                SubtreeLayoutScope layoutScope(box());
-                layoutScope.setNeedsLayout(&box(), LayoutInvalidationReason::ScrollbarChanged);
-                if (box().isLayoutBlock()) {
-                    LayoutBlock& block = toLayoutBlock(box());
-                    block.scrollbarsChanged(horizontalScrollBarChanged, verticalScrollBarChanged);
-                    block.layoutBlock(true);
+                if (delayedLayoutScope) {
+                    delayedLayoutScope->setNeedsLayout(&box(), LayoutInvalidationReason::ScrollbarChanged);
+                    didMarkForDelayedLayout = true;
                 } else {
-                    box().layout();
+                    SubtreeLayoutScope layoutScope(box());
+                    layoutScope.setNeedsLayout(&box(), LayoutInvalidationReason::ScrollbarChanged);
+                    if (box().isLayoutBlock()) {
+                        LayoutBlock& block = toLayoutBlock(box());
+                        block.scrollbarsChanged(horizontalScrollBarChanged, verticalScrollBarChanged);
+                        block.layoutBlock(true);
+                    } else {
+                        box().layout();
+                    }
                 }
                 LayoutObject* parent = box().parent();
                 if (parent && parent->isFlexibleBox())
@@ -727,6 +734,8 @@ void PaintLayerScrollableArea::updateAfterLayout()
 
     DisableCompositingQueryAsserts disabler;
     positionOverflowControls();
+
+    return didMarkForDelayedLayout;
 }
 
 ScrollBehavior PaintLayerScrollableArea::scrollBehaviorStyle() const

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

@@ -253,7 +253,9 @@ class CORE_EXPORT PaintLayerScrollableArea final : public NoBaseWillBeGarbageCol
         scrollToOffset(toDoubleSize(position), ScrollOffsetClamped, scrollBehavior, scrollType);
     }
 
-    void updateAfterLayout();
+    // Returns true if a layout object was marked for layout. In such a case, the layout scope's root
+    // should be laid out again.
+    bool updateAfterLayout(SubtreeLayoutScope* = nullptr);
     void updateAfterStyleChange(const ComputedStyle*);
     void updateAfterOverflowRecalc();