Bug 1359054 - Take shadow DOM into account when getting paint tree; r=maja_zf

We want to take shadow DOM into account when getting an element's
pointer-interactable paint tree.

Marionette is currently unable to determine if an element inside a shadow
DOM host is disconnected from the document because we are constructing
the frame container with only the main document.

MozReview-Commit-ID: IPDi8fQZYRP

--HG--
extra : rebase_source : 8c6757a032342aa6bbe50ef15025a37ac09ae413

testing/marionette/element.js

@@ -995,9 +995,17 @@ element.getInViewCentrePoint = function (rect, win) {
 element.getPointerInteractablePaintTree = function (el) {
   const doc = el.ownerDocument;
   const win = doc.defaultView;
+  const container = {frame: win};
+  const rootNode = el.getRootNode();
+
+  // Include shadow DOM host only if the element's root node is not the
+  // owner document.
+  if (rootNode !== doc) {
+    container.shadowRoot = rootNode;
+  }
 
   // pointer-interactable elements tree, step 1
-  if (element.isDisconnected(el, {frame: win})) {
+  if (element.isDisconnected(el, container)) {
     return [];
   }