Narrow VDA Decode() API and remove multi-frame tests.

ppapi/api/dev/ppb_video_decoder_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.
  */
 
 /**
  * This file defines the <code>PPB_VideoDecoder_Dev</code> interface.
  */
 label Chrome {
   M14 = 0.16
@@ skipping 44 matching lines @@
    * Returns true if is a video decoder, false otherwise.
    */
   PP_Bool IsVideoDecoder(
       [in] PP_Resource resource);
 
   /**
    * Dispatches bitstream buffer to the decoder.
    *
    * Parameters:
    *   |video_decoder| is the previously created handle to the decoder resource.
-   *   |bitstream_buffer| is the bitstream buffer that contains the input data.
+   *   |bitstream_buffer| is the bitstream buffer that contains at most one
+   *   input frame.
    *   |callback| will be called when |bitstream_buffer| has been processed by
    *   the decoder.
    *
    * Returns an error code from pp_errors.h.
    */
   int32_t Decode(
       [in] PP_Resource video_decoder,
       [in] PP_VideoBitstreamBuffer_Dev bitstream_buffer,
       [in] PP_CompletionCallback callback);
 
@@ skipping 69 matching lines @@
    * may be freed asynchronously, after this method returns no more callbacks
    * will be made on the client.  Any resources held by the client at that point
    * may be freed.
    *
    * Parameters:
    *   |video_decoder| is the previously created handle to the decoder resource.
    */
   void Destroy(
       [in] PP_Resource video_decoder);
 };