Enforce non-negative BitstreamBuffer id

ppapi/api/dev/pp_video_dev.idl

 /* Copyright (c) 2012 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.
  */
 
 /**
  * NOTE: these must be kept in sync with the versions in media/!
  */
 
 
@@ skipping 22 matching lines @@
   PP_VIDEODECODER_H264PROFILE_MULTIVIEWHIGH = 11,
   PP_VIDEODECODER_VP8PROFILE_MAIN = 12
 };
 
 /**
  * The data structure for video bitstream buffer.
  */
 [assert_size(12)]
 struct PP_VideoBitstreamBuffer_Dev {
   /**
-   * Client-specified identifier for the bitstream buffer.
+   * Client-specified identifier for the bitstream buffer. Valid values are
+   * non-negative.
    */
   int32_t id;
 
   /**
    * Buffer to hold the bitstream data. Should be allocated using the
    * PPB_Buffer interface for consistent interprocess behaviour.
    */
   PP_Resource data;
 
   /**
    * Size of the bitstream contained in buffer (in bytes).
    */
   uint32_t size;
 };
 
 /**
  * Struct for specifying texture-backed picture data.
  */
 [assert_size(16)]
 struct PP_PictureBuffer_Dev {
   /**
    * Client-specified id for the picture buffer. By using this value client can
    * keep track of the buffers it has assigned to the video decoder and how they
-   * are passed back to it.
+   * are passed back to it. Valid values are non-negative.
    */
   int32_t id;
 
   /**
    * Dimensions of the buffer.
    */
   PP_Size size;
 
   /**
    * Texture ID in the given context where picture is stored.
@@ skipping 39 matching lines @@
    */
   PP_VIDEODECODERERROR_UNREADABLE_INPUT = 3,
 
   /** 
    * A failure occurred at the browser layer or lower.  Examples of such
    * failures include GPU hardware failures, GPU driver failures, GPU library
    * failures, browser programming errors, and so on.
    */
   PP_VIDEODECODERERROR_PLATFORM_FAILURE = 4
 };