From de45820b64ab03768336c7242622ef9f499347cf Mon Sep 17 00:00:00 2001
From: "Matt A. Tobin" <email@mattatobin.com>
Date: Thu, 16 Apr 2020 20:19:06 -0400
Subject: Bug 1346623 - Allow anonymous content created with
 nsIDocument::InsertAnonymousContent can change from non-native to native AC

* Prevent canvas custom content from becoming NAC when reframing the root element
* Add an API to get computed style values through an AnonymousContent object

Tag #1375
---
 dom/base/AnonymousContent.cpp | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

(limited to 'dom/base/AnonymousContent.cpp')

diff --git a/dom/base/AnonymousContent.cpp b/dom/base/AnonymousContent.cpp
index 1df36b048..aea923f2b 100644
--- a/dom/base/AnonymousContent.cpp
+++ b/dom/base/AnonymousContent.cpp
@@ -7,6 +7,7 @@
 #include "AnonymousContent.h"
 #include "mozilla/dom/Element.h"
 #include "mozilla/dom/AnonymousContentBinding.h"
+#include "nsComputedDOMStyle.h"
 #include "nsCycleCollectionParticipant.h"
 #include "nsIDocument.h"
 #include "nsIDOMHTMLCollection.h"
@@ -208,5 +209,31 @@ AnonymousContent::WrapObject(JSContext* aCx,
   return AnonymousContentBinding::Wrap(aCx, this, aGivenProto, aReflector);
 }
 
+void
+AnonymousContent::GetComputedStylePropertyValue(const nsAString& aElementId,
+                                                const nsAString& aPropertyName,
+                                                DOMString& aResult,
+                                                ErrorResult& aRv)
+{
+  Element* element = GetElementById(aElementId);
+  if (!element) {
+    aRv.Throw(NS_ERROR_NOT_AVAILABLE);
+    return;
+  }
+
+  nsIPresShell* shell = element->OwnerDoc()->GetShell();
+  if (!shell) {
+    aRv.Throw(NS_ERROR_NOT_AVAILABLE);
+    return;
+  }
+
+  RefPtr<nsComputedDOMStyle> cs =
+    new nsComputedDOMStyle(element,
+                           NS_LITERAL_STRING(""),
+                           element->OwnerDoc(),
+                           nsComputedDOMStyle::eAll);
+  aRv = cs->GetPropertyValue(aPropertyName, aResult);
+}
+
 } // namespace dom
 } // namespace mozilla
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