Add comment to PPB_MouseInputEvent version 1.1 that GetMovement hasn't been supported.

ppapi/c/ppb_input_event.h

 /* Copyright (c) 2011 The Chromium Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 /* From ppb_input_event.idl modified Wed Aug 24 09:43:38 2011. */
 
 #ifndef PPAPI_C_PPB_INPUT_EVENT_H_
 #define PPAPI_C_PPB_INPUT_EVENT_H_
 
@@ skipping 457 matching lines @@
    * Returns the change in position of the mouse. When the mouse is locked,
    * although the mouse position doesn't actually change, this function
    * still provides movement information, which indicates what the change in
    * position would be had the mouse not been locked.
    *
    * @param[in] mouse_event A <code>PP_Resource</code> corresponding to a
    * mouse event.
    *
    * @return The change in position of the mouse, relative to the previous
    * position.
+   *
+   * TODO(yzshen): This feature hasn't been supported yet. The returned value is
+   * always (0, 0) for system-generated mouse events (which are passed through
+   * the <code>HandleInputEvent</code>).
    */
   struct PP_Point (*GetMovement)(PP_Resource mouse_event);
 };
 
 struct PPB_MouseInputEvent_1_0 {
   PP_Resource (*Create)(PP_Instance instance,
                         PP_InputEvent_Type type,
                         PP_TimeTicks time_stamp,
                         uint32_t modifiers,
                         PP_InputEvent_MouseButton mouse_button,
@@ skipping 181 matching lines @@
    * undefined var.
    */
   struct PP_Var (*GetCharacterText)(PP_Resource character_event);
 };
 /**
  * @}
  */
 
 #endif  /* PPAPI_C_PPB_INPUT_EVENT_H_ */