Make Screen Orientation use Platform Events in order to handle polling.

public/platform/Platform.h

Index: public/platform/Platform.h
diff --git a/public/platform/Platform.h b/public/platform/Platform.h
index 41343b51fef518693040bc7575e89d3579214a61..ce362799c9c079d4fd1e563bc8f24de9705e5448 100644
--- a/public/platform/Platform.h
+++ b/public/platform/Platform.h
@@ -621,6 +621,9 @@ public:
         case blink::WebPlatformEventGamepad:
             setGamepadListener(static_cast<blink::WebGamepadListener*>(listener));
             break;
+        case blink::WebPlatformEventScreenOrientation:
+            // No backward-compatibility support here.
+            break;
         }
     }
 
@@ -646,6 +649,9 @@ public:
         case blink::WebPlatformEventGamepad:
             setGamepadListener(0);
             break;
+        case blink::WebPlatformEventScreenOrientation:
+            // No backward-compatibility support here.
+            break;
         }
     }