[css-grid] Fix crash removing positioned grid item

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

Index: third_party/WebKit/Source/core/layout/LayoutGrid.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutGrid.cpp b/third_party/WebKit/Source/core/layout/LayoutGrid.cpp
index 554dd56f02e6a7f27964a87cb991eb8c92460a91..84c9f19e65f8ecc7f2c510b236b9d2b6cd733bb3 100644
--- a/third_party/WebKit/Source/core/layout/LayoutGrid.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutGrid.cpp
@@ -76,6 +76,12 @@ LayoutGrid* LayoutGrid::createAnonymous(Document* document) {
 void LayoutGrid::addChild(LayoutObject* newChild, LayoutObject* beforeChild) {
   LayoutBlock::addChild(newChild, beforeChild);
 
+  // Positioned grid items do not take up space or otherwise participate in the
+  // layout of the grid, for that reason we don't need to mark the grid as dirty
+  // when they are added.
+  if (newChild->isOutOfFlowPositioned())
+    return;
+
   // The grid needs to be recomputed as it might contain auto-placed items that
   // will change their position.
   dirtyGrid();
@@ -84,6 +90,12 @@ void LayoutGrid::addChild(LayoutObject* newChild, LayoutObject* beforeChild) {
 void LayoutGrid::removeChild(LayoutObject* child) {
   LayoutBlock::removeChild(child);
 
+  // Positioned grid items do not take up space or otherwise participate in the
+  // layout of the grid, for that reason we don't need to mark the grid as dirty
+  // when they are removed.
+  if (child->isOutOfFlowPositioned())
+    return;
+
   // The grid needs to be recomputed as it might contain auto-placed items that
   // will change their position.
   dirtyGrid();