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

ppapi/cpp/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.
 
 #ifndef PPAPI_CPP_INPUT_EVENT_H_
 #define PPAPI_CPP_INPUT_EVENT_H_
 
 #include <string>
 
 #include "ppapi/c/ppb_input_event.h"
@@ skipping 141 matching lines @@
   // TODO(brettw) figure out exactly what this means.
   int32_t GetClickCount() const;
 
   /// 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.
   ///
   /// @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>).
   Point GetMovement() const;
 };
 
 class WheelInputEvent : public InputEvent {
  public:
   /// Constructs an is_null() wheel input event object.
   WheelInputEvent();
 
   /// This constructor constructs a wheel input event object from the
   /// provided generic input event. If the given event is itself
@@ skipping 122 matching lines @@
   ///
   /// @return A string var representing a single typed character for character
   /// input events. For non-character input events the return value will be an
   /// undefined var.
   Var GetCharacterText() const;
 };
 
 }  // namespace pp
 
 #endif  // PPAPI_CPP_INPUT_EVENT_H_