Implement the Blink part of the Device Motion API.

public/platform/Platform.h

Index: public/platform/Platform.h
diff --git a/public/platform/Platform.h b/public/platform/Platform.h
index 566305709c633907bf65e267ca185e78e0b2df96..273e646f7100b60b79f513e52ea0dfe7afb7fc45 100644
--- a/public/platform/Platform.h
+++ b/public/platform/Platform.h
@@ -54,6 +54,7 @@ class WebBlobRegistry;
 class WebClipboard;
 class WebCompositorSupport;
 class WebCookieJar;
+class WebDeviceMotionListener;
 class WebDiscardableMemory;
 class WebFallbackThemeEngine;
 class WebFileSystem;
@@ -510,6 +511,13 @@ public:
     virtual void didStartWorkerRunLoop(const WebWorkerRunLoop&) { }
     virtual void didStopWorkerRunLoop(const WebWorkerRunLoop&) { }
 
+
+    // Device Motion / Orientation ----------------------------------------
+
+    // Sets a Listener to listen for device motion data updates.
+    // If null, the platform stops providing device motion data to the current listener.
+    virtual void setDeviceMotionListener(WebKit::WebDeviceMotionListener*) { }
+
 protected:
     virtual ~Platform() { }
 };