PPAPI: Add missing const to AudioConfig::sample_frame_count().

ppapi/cpp/audio_config.h

 // 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.
 
 #ifndef PPAPI_CPP_AUDIO_CONFIG_H_
 #define PPAPI_CPP_AUDIO_CONFIG_H_
 
 #include "ppapi/c/ppb_audio_config.h"
 #include "ppapi/c/pp_stdint.h"
 #include "ppapi/cpp/resource.h"
@@ skipping 102 matching lines @@
 
   /// Getter function for returning the internal
   /// <code>PP_AudioSampleRate</code> enum.
   ///
   /// @return The <code>PP_AudioSampleRate</code> enum.
   PP_AudioSampleRate sample_rate() const { return sample_rate_; }
 
   /// Getter function for returning the internal sample frame count.
   ///
   /// @return A uint32_t containing the sample frame count.
-  uint32_t sample_frame_count() { return sample_frame_count_; }
+  uint32_t sample_frame_count() const { return sample_frame_count_; }
 
  private:
   PP_AudioSampleRate sample_rate_;
   uint32_t sample_frame_count_;
 };
 
 }  // namespace pp
 
 #endif  // PPAPI_CPP_AUDIO_CONFIG_H_