Stop firing orientationchange events at pages that are not visible

Source/modules/screen_orientation/ScreenOrientationController.h

Index: Source/modules/screen_orientation/ScreenOrientationController.h
diff --git a/Source/modules/screen_orientation/ScreenOrientationController.h b/Source/modules/screen_orientation/ScreenOrientationController.h
index b5f8de70869c5961b30f91390bf6b1852267b379..975da074686f9a542282baae08f6365f903800ca 100644
--- a/Source/modules/screen_orientation/ScreenOrientationController.h
+++ b/Source/modules/screen_orientation/ScreenOrientationController.h
@@ -6,13 +6,14 @@
 #define ScreenOrientationController_h
 
 #include "core/dom/DocumentSupplementable.h"
+#include "core/page/PageLifecycleObserver.h"
 #include "public/platform/WebScreenOrientationType.h"
 
 namespace WebCore {
 
 class FrameView;
 
-class ScreenOrientationController FINAL : public NoBaseWillBeGarbageCollected<ScreenOrientationController>, public DocumentSupplement {
+class ScreenOrientationController FINAL : public NoBaseWillBeGarbageCollected<ScreenOrientationController>, public DocumentSupplement, public PageLifecycleObserver {
     WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(ScreenOrientationController);
     DECLARE_EMPTY_VIRTUAL_DESTRUCTOR_WILL_BE_REMOVED(ScreenOrientationController);
 public:
@@ -26,7 +27,11 @@ private:
     explicit ScreenOrientationController(Document&);
     static blink::WebScreenOrientationType computeOrientation(FrameView*);
 
+    // Inherited from PageLifecycleObserver.
+    virtual void pageVisibilityChanged() OVERRIDE;
+
     Document& m_document;
+    blink::WebScreenOrientationType m_overrideOrientation;
 };
 
 } // namespace WebCore