Bug 1498860 - Add window.screenLeft / window.screenTop as aliases of screenX / screenY. r=smaug

Tests are at https://github.com/web-platform-tests/wpt/pull/13543.

Spec is waiting on those, but this matches all other browsers.

Differential Revision: https://phabricator.services.mozilla.com/D8917

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

dom/base/nsGlobalWindowInner.h

@@ -816,6 +816,19 @@ public:
   {
     return GetScrollY(aError);
   }
+
+  int32_t GetScreenLeft(mozilla::dom::CallerType aCallerType,
+                        mozilla::ErrorResult& aError)
+  {
+    return GetScreenX(aCallerType, aError);
+  }
+
+  int32_t GetScreenTop(mozilla::dom::CallerType aCallerType,
+                       mozilla::ErrorResult& aError)
+  {
+    return GetScreenY(aCallerType, aError);
+  }
+
   void GetScreenX(JSContext* aCx, JS::MutableHandle<JS::Value> aValue,
                   mozilla::dom::CallerType aCallerType,
                   mozilla::ErrorResult& aError);

dom/webidl/Window.webidl

@@ -188,6 +188,10 @@ partial interface Window {
   [Replaceable, Throws] readonly attribute double scrollY;
   [Replaceable, Throws] readonly attribute double pageYOffset;
 
+  // Aliases for screenX / screenY.
+  [Replaceable, Throws, NeedsCallerType] readonly attribute double screenLeft;
+  [Replaceable, Throws, NeedsCallerType] readonly attribute double screenTop;
+
   // client
   // These are writable because we allow chrome to write them.  And they need
   // to use 'any' as the type, because non-chrome writing them needs to act