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

3 files changed, 40 insertions, 0 deletions

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
diff --git a/dom/base/AnonymousContent.h b/dom/base/AnonymousContent.h
index fd3b59c44..b56c14595 100644
--- a/dom/base/AnonymousContent.h
+++ b/dom/base/AnonymousContent.h
@@ -68,6 +68,11 @@ public:
                                 const Sequence<OwningNonNull<DOMRect>>& aRects,
                                 ErrorResult& aError);
 
+  void GetComputedStylePropertyValue(const nsAString& aElementId,
+                                     const nsAString& aPropertyName,
+                                     DOMString& aResult,
+                                     ErrorResult& aRv);
+
 private:
   ~AnonymousContent();
   nsCOMPtr<Element> mContentNode;
diff --git a/dom/webidl/AnonymousContent.webidl b/dom/webidl/AnonymousContent.webidl
index 6755fe598..8be69cd26 100644
--- a/dom/webidl/AnonymousContent.webidl
+++ b/dom/webidl/AnonymousContent.webidl
@@ -77,4 +77,12 @@ interface AnonymousContent {
   [Throws]
   void setCutoutRectsForElement(DOMString elementId,
                                 sequence<DOMRect> rects);
+
+  /**
+   * Get the computed value of a property on an element inside this custom
+   * anonymous content.
+   */
+  [Throws]
+  DOMString? getComputedStylePropertyValue(DOMString elementId,
+                                           DOMString propertyName);
 };