Add plumbing for testing API for MockWebDeviceMotionHandler injection.

webkit/support/webkit_support.cc

Index: webkit/support/webkit_support.cc
diff --git a/webkit/support/webkit_support.cc b/webkit/support/webkit_support.cc
index e2c9bf3774499834780a8f163bfb490399b7d57f..0fa71488cda35b36df76610032dfcf0b42d71080 100644
--- a/webkit/support/webkit_support.cc
+++ b/webkit/support/webkit_support.cc
@@ -843,4 +843,9 @@ void SetGamepadData(const WebKit::WebGamepads& pads) {
   test_environment->webkit_platform_support()->setGamepadData(pads);
 }
 
+void SetDeviceMotionListener(WebKit::WebDeviceMotionListener* listener) {
+  test_environment->webkit_platform_support()
+      ->setDeviceMotionListener(listener);
+}
+
 }  // namespace webkit_support