Implement the Blink part of the Device Motion API.

Source/Platform/chromium/public/Platform.h

Index: Source/Platform/chromium/public/Platform.h
diff --git a/Source/Platform/chromium/public/Platform.h b/Source/Platform/chromium/public/Platform.h
index 566305709c633907bf65e267ca185e78e0b2df96..be0b53beb2745ccb5a289e6f1ba499d1f4f547d5 100644
--- a/Source/Platform/chromium/public/Platform.h
+++ b/Source/Platform/chromium/public/Platform.h
@@ -54,6 +54,7 @@ class WebBlobRegistry;
 class WebClipboard;
 class WebCompositorSupport;
 class WebCookieJar;
+class WebDeviceMotionHandler;
 class WebDiscardableMemory;
 class WebFallbackThemeEngine;
 class WebFileSystem;
@@ -510,6 +511,10 @@ public:
     virtual void didStartWorkerRunLoop(const WebWorkerRunLoop&) { }
     virtual void didStopWorkerRunLoop(const WebWorkerRunLoop&) { }
 
+    // Device Motion / Orientation ----------------------------------------
+
+    virtual WebDeviceMotionHandler* deviceMotionHandler() { return 0; }
+
 protected:
     virtual ~Platform() { }
 };