Bug 1658469 - Don't clone UA widgets for printing. r=smaug

We run the widget initialization code regardless on bind, and some of it
doesn't deal with shadow roots being already populated.

Differential Revision: https://phabricator.services.mozilla.com/D86952

dom/base/ShadowRoot.cpp

@@ -95,6 +95,8 @@ JSObject* ShadowRoot::WrapNode(JSContext* aCx,
 }
 
 void ShadowRoot::CloneInternalDataFrom(ShadowRoot* aOther) {
+  MOZ_ASSERT(!aOther->IsUAWidget());
+
   size_t sheetCount = aOther->SheetCount();
   for (size_t i = 0; i < sheetCount; ++i) {
     StyleSheet* sheet = aOther->SheetAt(i);

dom/base/nsINode.cpp

@@ -3305,7 +3305,7 @@ already_AddRefed<nsINode> nsINode::CloneAndAdopt(
 
         // Clone the Shadow DOM
         ShadowRoot* originalShadowRoot = aNode->AsElement()->GetShadowRoot();
-        if (originalShadowRoot) {
+        if (originalShadowRoot && !originalShadowRoot->IsUAWidget()) {
           RefPtr<ShadowRoot> newShadowRoot =
               clone->AsElement()->AttachShadowWithoutNameChecks(
                   originalShadowRoot->Mode());

layout/base/tests/chrome/printpreview_helper.xhtml

@@ -424,7 +424,7 @@ async function compareFiles(src1, src2, options = {}) {
 
   await new Promise((resolve) => {
     iframeElement.addEventListener("load", resolve, { capture: true, once: true });
-    iframeElement.setAttribute("src", BASE + src1);
+    iframeElement.setAttribute("src", new URL(src1, BASE).href);
   });
 
   if (messagePromise) {
@@ -438,7 +438,7 @@ async function compareFiles(src1, src2, options = {}) {
 
   await new Promise((resolve) => {
     iframeElement.addEventListener("load", resolve, { capture: true, once: true });
-    iframeElement.setAttribute("src", BASE + src2);
+    iframeElement.setAttribute("src", new URL(src2, BASE).href);
   });
 
   await printpreview(options.ref || options);
@@ -551,6 +551,11 @@ async function runTest20() {
 
   exitprintpreview();
 
+  requestAnimationFrame(() => setTimeout(runTest21));
+}
+
+async function runTest21() {
+  await compareFiles("data:text/html,<audio controls>", "data:text/html,<audio controls >"); // Shouldn't crash.
   finish();
 }