Update screen.orientation to follow the latest version of the specs.

Source/modules/screen_orientation/ScreenOrientation.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "modules/screen_orientation/ScreenOrientation.h"
 
 #include "core/frame/DOMWindow.h"
 #include "core/frame/LocalFrame.h"
 #include "core/frame/Screen.h"
@@ skipping 106 matching lines @@
     return *supplement;
 }
 
 ScreenOrientation::~ScreenOrientation()
 {
 }
 
 const AtomicString& ScreenOrientation::orientation(Screen& screen)
 {
     ScreenOrientation& screenOrientation = ScreenOrientation::from(screen);
-    if (!screenOrientation.document())
-        return emptyAtom;
+    if (!screenOrientation.document()) {
+        // FIXME: we should try to return a better guess, like the latest known value.
+        return orientationToString(blink::WebScreenOrientationPortraitPrimary);
+    }
     ScreenOrientationController& controller = ScreenOrientationController::from(*screenOrientation.document());
     return orientationToString(controller.orientation());
 }
 
 bool ScreenOrientation::lockOrientation(Screen& screen, const AtomicString& orientationString)
 {
     blink::WebScreenOrientations orientations = stringToOrientations(orientationString);
     if (!orientations)
         return false;
     ScreenOrientation::from(screen).lockOrientationAsync(orientations);
     return true;
 }
 
 void ScreenOrientation::unlockOrientation(Screen& screen)
 {
     ScreenOrientation::from(screen).lockOrientationAsync(WebScreenOrientationDefault);
 }
 
 } // namespace WebCore