Added support of relative mouse motion in Chromoting.

remoting/host/input_injector_linux.cc

Index: remoting/host/input_injector_linux.cc
diff --git a/remoting/host/input_injector_linux.cc b/remoting/host/input_injector_linux.cc
index cbb807bdc3a65aaed001f500244caaff0bc85517..d61d8f2072441dab7370ec31156969f659bd594a 100644
--- a/remoting/host/input_injector_linux.cc
+++ b/remoting/host/input_injector_linux.cc
@@ -299,7 +299,16 @@ void InputInjectorLinux::Core::InjectMouseEvent(const MouseEvent& event) {
     return;
   }
 
-  if (event.has_x() && event.has_y()) {
+  if (event.has_delta_x() &&
+      event.has_delta_y() &&
+      (event.delta_x() != 0 || event.delta_y() != 0)) {
+    latest_mouse_position_ = SkIPoint::Make(-1, -1);
+    VLOG(3) << "Moving mouse by " << event.delta_x() << "," << event.delta_y();
+    XTestFakeRelativeMotionEvent(display_,
+                                 event.delta_x(), event.delta_y(),
+                                 CurrentTime);
+
+  } else if (event.has_x() && event.has_y()) {
     // Injecting a motion event immediately before a button release results in
     // a MotionNotify even if the mouse position hasn't changed, which confuses
     // apps which assume MotionNotify implies movement. See crbug.com/138075.