Allow any self-painting layer to be considered for being a relayout root.

As of this commit [1], it was previously limited to positioned elements.

[1] https://chromium.googlesource.com/chromium/src/+/0a7940331530fc647dbd37e6bcce20540271234a

Bug: 1087177

Change-Id: Ief3013338d63b59a88a788fced0e185e293de850
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2219312Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#772560}

third_party/blink/renderer/core/layout/layout_object.cc

@@ -923,7 +923,10 @@ static inline bool ObjectIsRelayoutBoundary(const LayoutObject* object) {
   // Positioned objects always have self-painting layers and are safe to use as
   // relayout boundaries.
   bool is_svg_root = object->IsSVGRoot();
-  if (!object->IsPositioned() && !is_svg_root)
+  bool has_self_painting_layer =
+      object->HasLayer() &&
+      ToLayoutBoxModelObject(object)->HasSelfPaintingLayer();
+  if (!has_self_painting_layer && !is_svg_root)
     return false;
 
   // LayoutInline can't be relayout roots since LayoutBlockFlow is responsible

third_party/blink/renderer/core/layout/layout_object_test.cc

@@ -1117,4 +1117,21 @@ TEST_F(LayoutObjectTest, NeedsLayoutOverflowRecalc) {
   EXPECT_FALSE(other->NeedsLayoutOverflowRecalc());
 }
 
+TEST_F(LayoutObjectTest, ContainValueIsRelayoutBoundary) {
+  SetBodyInnerHTML(R"HTML(
+    <div id='target1' style='contain:layout'></div>
+    <div id='target2' style='contain:layout size'></div>
+    <div id='target3' style='contain:paint'></div>
+    <div id='target4' style='contain:size'></div>
+    <div id='target5' style='contain:content'></div>
+    <div id='target6' style='contain:strict'></div>
+  )HTML");
+  EXPECT_FALSE(GetLayoutObjectByElementId("target1")->IsRelayoutBoundary());
+  EXPECT_TRUE(GetLayoutObjectByElementId("target2")->IsRelayoutBoundary());
+  EXPECT_FALSE(GetLayoutObjectByElementId("target3")->IsRelayoutBoundary());
+  EXPECT_FALSE(GetLayoutObjectByElementId("target4")->IsRelayoutBoundary());
+  EXPECT_FALSE(GetLayoutObjectByElementId("target5")->IsRelayoutBoundary());
+  EXPECT_TRUE(GetLayoutObjectByElementId("target6")->IsRelayoutBoundary());
+}
+
 }  // namespace blink