Bug 999297 - Implement xpc::UnwrapReflectorToISupports. r=bz

I kind of thought we already had something like this, but I couldn't find
anything.

js/xpconnect/src/nsXPConnect.cpp

@@ -628,28 +628,34 @@ nsXPConnect::GetWrappedNativeOfJSObject(JSContext * aJSContext,
     return NS_OK;
 }
 
+nsISupports*
+xpc::UnwrapReflectorToISupports(JSObject *reflector)
+{
+    // Unwrap security wrappers, if allowed.
+    reflector = js::CheckedUnwrap(reflector, /* stopAtOuter = */ false);
+    if (!reflector)
+        return nullptr;
+
+    // Try XPCWrappedNatives.
+    if (IS_WN_REFLECTOR(reflector)) {
+        XPCWrappedNative *wn = XPCWrappedNative::Get(reflector);
+        if (!wn)
+            return nullptr;
+        return wn->Native();
+    }
+
+    // Try DOM objects.
+    nsCOMPtr<nsISupports> canonical =
+        do_QueryInterface(mozilla::dom::UnwrapDOMObjectToISupports(reflector));
+    return canonical;
+}
+
 /* nsISupports getNativeOfWrapper(in JSContextPtr aJSContext, in JSObjectPtr  aJSObj); */
 NS_IMETHODIMP_(nsISupports*)
 nsXPConnect::GetNativeOfWrapper(JSContext *aJSContext,
                                 JSObject *aJSObj)
 {
-    MOZ_ASSERT(aJSContext, "bad param");
-    MOZ_ASSERT(aJSObj, "bad param");
-
-    aJSObj = js::CheckedUnwrap(aJSObj, /* stopAtOuter = */ false);
-    if (!aJSObj) {
-        JS_ReportError(aJSContext, "Permission denied to get native of security wrapper");
-        return nullptr;
-    }
-    if (IS_WN_REFLECTOR(aJSObj)) {
-        if (XPCWrappedNative *wn = XPCWrappedNative::Get(aJSObj))
-            return wn->Native();
-        return nullptr;
-    }
-
-    nsCOMPtr<nsISupports> canonical =
-        do_QueryInterface(mozilla::dom::UnwrapDOMObjectToISupports(aJSObj));
-    return canonical;
+    return UnwrapReflectorToISupports(aJSObj);
 }
 
 /* nsIXPConnectWrappedNative getWrappedNativeOfNativeObject (in JSContextPtr aJSContext, in JSObjectPtr aScope, in nsISupports aCOMObj, in nsIIDRef aIID); */

js/xpconnect/src/xpcprivate.h

@@ -2540,6 +2540,9 @@ public:
                                          const nsID* iid,
                                          nsISupports* aOuter,
                                          nsresult* pErr);
+
+    // Note - This return the XPCWrappedNative, rather than the native itself,
+    // for the WN case. You probably want UnwrapReflectorToISupports.
     static bool GetISupportsFromJSObject(JSObject* obj, nsISupports** iface);
 
     /**

js/xpconnect/src/xpcpublic.h

@@ -413,6 +413,13 @@ Throw(JSContext *cx, nsresult rv);
 nsIGlobalObject *
 GetNativeForGlobal(JSObject *global);
 
+/**
+ * Returns the nsISupports native behind a given reflector (either DOM or
+ * XPCWN).
+ */
+nsISupports *
+UnwrapReflectorToISupports(JSObject *reflector);
+
 /**
  * In some cases a native object does not really belong to any compartment (XBL,
  * document created from by XHR of a worker, etc.). But when for some reason we