Add plumbing for testing API for MockWebDeviceMotionHandler injection.

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 d80123d3a28ab52eab1cc5b650f7d583d09c4314..13595bb3522048f8779a2448c14f10c8f8097c04 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 WebDeviceMotionListener;
 class WebGamepads;
 struct WebSize;
 }
@@ -30,6 +31,10 @@ void EnableWebTestProxyCreation(const base::Callback<
 // WebKitPlatformSupport::sampleGamepads().
 void SetMockGamepads(const WebKit::WebGamepads& pads);
 
+// Sets the WebDeviceMotionListener that should be used when registering
+// a listener through WebKitPlatformSupport::setDeviceMotionListener().
+void SetMockDeviceMotionListener(WebKit::WebDeviceMotionListener* listener);
+
 // Disable logging to the console from the appcache system.
 void DisableAppCacheLogging();