Add plumbing for platform based Device Motion testing.

content/public/test/layouttest_support.h

Index: content/public/test/layouttest_support.h
diff --git a/content/public/test/layouttest_support.h b/content/public/test/layouttest_support.h
index 5ae7396e7cc4c1a1d0ff463ee7f7498b0b7ee3d4..01577bd48514131b59b16017640cd1dea6ae2a05 100644
--- a/content/public/test/layouttest_support.h
+++ b/content/public/test/layouttest_support.h
@@ -8,6 +8,7 @@
 #include "base/callback_forward.h"
 
 namespace WebKit {
+class WebDeviceMotionData;
 class WebGamepads;
 struct WebSize;
 }
@@ -39,6 +40,10 @@ void EnableWebTestProxyCreation(const base::Callback<
 // WebKitPlatformSupport::sampleGamepads().
 void SetMockGamepads(const WebKit::WebGamepads& pads);
 
+// Sets WebDeviceMotionData that should be used when registering
+// a listener through WebKitPlatformSupport::setDeviceMotionListener().
+void SetMockDeviceMotionData(const WebKit::WebDeviceMotionData& data);
+
 // Returns the length of the local session history of a render view.
 int GetLocalSessionHistoryLength(RenderView* render_view);