[Isolation]: Establish isolation on style & layout containment.

This patch adds style & layout containment as another criteria for when
we establish isolation.

R=chrishtr@chromium.org

Change-Id: I325edc499d41ea8580d138e982a358f74d13f22e
Reviewed-on: https://chromium-review.googlesource.com/c/1388747Reviewed-by: Mason Freed <masonfreed@chromium.org>
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: vmpstr <vmpstr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619964}

third_party/blink/renderer/core/paint/paint_property_tree_builder.cc

@@ -317,8 +317,12 @@ static bool NeedsIsolationNodes(const LayoutObject& object) {
     return false;
 
   // Paint containment establishes isolation.
-  if (object.ShouldApplyPaintContainment())
+  // Style & Layout containment also establish isolation.
+  if (object.ShouldApplyPaintContainment() ||
+      (object.ShouldApplyStyleContainment() &&
+       object.ShouldApplyLayoutContainment())) {
     return true;
+  }
 
   // Layout view establishes isolation with the exception of local roots (since
   // they are already essentially isolated).