Bug 1484474 - Make the ua widget flag in ShadowRoot write-only. r=smaug

Letting people set it back to false would be bad.

Differential Revision: https://phabricator.services.mozilla.com/D3714

--HG--
extra : moz-landing-system : lando

dom/base/ShadowRoot.cpp

@@ -120,12 +120,6 @@ ShadowRoot::SetIsComposedDocParticipant(bool aIsComposedDocParticipant)
   }
 }
 
-void
-ShadowRoot::SetIsUAWidget(bool aIsUAWidget)
-{
-  mIsUAWidget = aIsUAWidget;
-}
-
 JSObject*
 ShadowRoot::WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto)
 {
@@ -563,7 +557,6 @@ ShadowRoot::ImportNodeAndAppendChildAt(nsINode& aParentNode,
                                        mozilla::ErrorResult& rv)
 {
   MOZ_ASSERT(mIsUAWidget);
-  MOZ_ASSERT(OwnerDoc());
 
   if (!aParentNode.IsInUAWidget()) {
     rv.Throw(NS_ERROR_INVALID_ARG);

dom/base/ShadowRoot.h

@@ -197,7 +197,10 @@ public:
     return mIsUAWidget;
   }
 
-  void SetIsUAWidget(bool aIsUAWidget);
+  void SetIsUAWidget()
+  {
+    mIsUAWidget = true;
+  }
 
   void GetEventTargetParent(EventChainPreVisitor& aVisitor) override;
 

dom/html/HTMLMediaElement.cpp

@@ -4950,7 +4950,7 @@ HTMLMediaElement::AttachAndSetUAShadowRoot()
   // Add a closed shadow root to host video controls
   RefPtr<ShadowRoot> shadowRoot =
     AttachShadowWithoutNameChecks(ShadowRootMode::Closed);
-  shadowRoot->SetIsUAWidget(true);
+  shadowRoot->SetIsUAWidget();
 }
 
 nsresult

dom/webidl/ShadowRoot.webidl

@@ -47,7 +47,7 @@ interface ShadowRoot : DocumentFragment
 
   // For triggering UA Widget scope in tests.
   [ChromeOnly]
-  void setIsUAWidget(boolean isUAWidget);
+  void setIsUAWidget();
 };
 
 ShadowRoot implements DocumentOrShadowRoot;

toolkit/content/tests/widgets/test_ua_widget.html

@@ -21,7 +21,7 @@ const content = document.getElementById("content");
 
 const div = content.appendChild(document.createElement("div"));
 div.attachShadow({ mode: "open"});
-SpecialPowers.wrap(div.shadowRoot).setIsUAWidget(true);
+SpecialPowers.wrap(div.shadowRoot).setIsUAWidget();
 
 const sandbox = SpecialPowers.Cu.getUAWidgetScope(SpecialPowers.wrap(div).nodePrincipal);