Reland main thread position sticky implementation.

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

Index: third_party/WebKit/Source/core/layout/LayoutBlock.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBlock.cpp b/third_party/WebKit/Source/core/layout/LayoutBlock.cpp
index 24154469a213ee910a2faf91521f742e44581f37..5b1bf91dd065a1c214c59c753fc35394dc74636c 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBlock.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBlock.cpp
@@ -365,6 +365,9 @@ void LayoutBlock::updateFromStyle()
 
     bool shouldClipOverflow = !styleRef().isOverflowVisible() && allowsOverflowClip();
     if (shouldClipOverflow != hasOverflowClip()) {
+        if (!shouldClipOverflow)
+            getScrollableArea()->invalidateAllStickyConstraints();
+
         // 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 = firstChild(); child; child = child->nextSibling())
@@ -840,8 +843,12 @@ bool LayoutBlock::finishDelayUpdateScrollInfo(SubtreeLayoutScope* layoutScope, S
     return childrenMarkedForRelayout;
 }
 
-void LayoutBlock::updateScrollInfoAfterLayout()
+void LayoutBlock::updateAfterLayout()
 {
+    invalidateStickyConstraints();
+
+    // Update our scroll information if we're overflow:auto/scroll/hidden now that we know if
+    // we overflow or not.
     if (hasOverflowClip()) {
         if (style()->isFlippedBlocksWritingMode()) {
             // FIXME: https://bugs.webkit.org/show_bug.cgi?id=97937
@@ -1084,7 +1091,7 @@ bool LayoutBlock::simplifiedLayout()
 
     updateLayerTransformAfterLayout();
 
-    updateScrollInfoAfterLayout();
+    updateAfterLayout();
 
     clearNeedsLayout();