Bug 1478806. Remove nsIBrowserElementNextPaintListener. r=mccr8

There's no particular reason for us to have this interface.  The only consumer
is JS-implemented, and the only caller has JS values to start with; we can just
pass these as jsval.

dom/browser-element/BrowserElementParent.js

@@ -796,7 +796,7 @@ BrowserElementParent.prototype = {
     this._nextPaintListeners = [];
     for (let listener of listeners) {
       try {
-        listener.recvNextPaint();
+        listener();
       } catch (e) {
         // If a listener throws we'll continue.
       }

dom/browser-element/nsIBrowserElementAPI.idl

@@ -9,12 +9,6 @@
 webidl DOMRequest;
 webidl FrameLoader;
 
-[scriptable, function, uuid(00d0e19d-bd67-491f-8e85-b9905224d3bb)]
-interface nsIBrowserElementNextPaintListener : nsISupports
-{
-  void recvNextPaint();
-};
-
 %{C++
 #define BROWSER_ELEMENT_API_CONTRACTID "@mozilla.org/dom/browser-element-api;1"
 #define BROWSER_ELEMENT_API_CID                                 \
@@ -77,8 +71,8 @@ interface nsIBrowserElementAPI : nsISupports
   void findNext(in long direction);
   void clearMatch();
 
-  void addNextPaintListener(in nsIBrowserElementNextPaintListener listener);
-  void removeNextPaintListener(in nsIBrowserElementNextPaintListener listener);
+  void addNextPaintListener(in jsval listener); // BrowserElementNextPaintEventCallback
+  void removeNextPaintListener(in jsval listener); // BrowserElementNextPaintEventCallback
 
   DOMRequest executeScript(in DOMString script, in jsval options);
 

dom/html/nsBrowserElement.cpp

@@ -368,11 +368,9 @@ nsBrowserElement::AddNextPaintListener(BrowserElementNextPaintEventCallback& aLi
 {
   NS_ENSURE_TRUE_VOID(IsBrowserElementOrThrow(aRv));
 
-  CallbackObjectHolder<BrowserElementNextPaintEventCallback,
-                       nsIBrowserElementNextPaintListener> holder(&aListener);
-  nsCOMPtr<nsIBrowserElementNextPaintListener> listener = holder.ToXPCOMCallback();
-
-  nsresult rv = mBrowserElementAPI->AddNextPaintListener(listener);
+  JS::Rooted<JS::Value> val(RootingCx(),
+                            JS::ObjectOrNullValue(aListener.CallbackOrNull()));
+  nsresult rv = mBrowserElementAPI->AddNextPaintListener(val);
 
   if (NS_WARN_IF(NS_FAILED(rv))) {
     aRv.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
@@ -385,11 +383,9 @@ nsBrowserElement::RemoveNextPaintListener(BrowserElementNextPaintEventCallback&
 {
   NS_ENSURE_TRUE_VOID(IsBrowserElementOrThrow(aRv));
 
-  CallbackObjectHolder<BrowserElementNextPaintEventCallback,
-                       nsIBrowserElementNextPaintListener> holder(&aListener);
-  nsCOMPtr<nsIBrowserElementNextPaintListener> listener = holder.ToXPCOMCallback();
-
-  nsresult rv = mBrowserElementAPI->RemoveNextPaintListener(listener);
+  JS::Rooted<JS::Value> val(RootingCx(),
+                            JS::ObjectOrNullValue(aListener.CallbackOrNull()));
+  nsresult rv = mBrowserElementAPI->RemoveNextPaintListener(val);
 
   if (NS_WARN_IF(NS_FAILED(rv))) {
     aRv.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);