Update BufferedDataSource class documentation.

media/blink/buffered_data_source.cc

 // Copyright 2013 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.
 
 #include "media/blink/buffered_data_source.h"
 
 #include "base/bind.h"
 #include "base/callback_helpers.h"
 #include "base/location.h"
 #include "base/single_thread_task_runner.h"
@@ skipping 86 matching lines @@
       media_has_played_(false),
       preload_(AUTO),
       bitrate_(0),
       playback_rate_(0.0),
       media_log_(media_log),
       host_(host),
       downloading_cb_(downloading_cb),
       weak_factory_(this) {
   DCHECK(host_);
   DCHECK(!downloading_cb_.is_null());
+  DCHECK(render_task_runner_->BelongsToCurrentThread());
 }
 
-BufferedDataSource::~BufferedDataSource() {}
+BufferedDataSource::~BufferedDataSource() {
+  DCHECK(render_task_runner_->BelongsToCurrentThread());
+}
 
 // A factory method to create BufferedResourceLoader using the read parameters.
 // This method can be overridden to inject mock BufferedResourceLoader object
 // for testing purpose.
 BufferedResourceLoader* BufferedDataSource::CreateResourceLoader(
     int64 first_byte_position, int64 last_byte_position) {
   DCHECK(render_task_runner_->BelongsToCurrentThread());
 
   BufferedResourceLoader::DeferStrategy strategy = preload_ == METADATA ?
       BufferedResourceLoader::kReadThenDefer :
@@ skipping 407 matching lines @@
   }
 
   // If media is currently playing or the page indicated preload=auto or the
   // the server does not support the byte range request or we do not want to go
   // too far ahead of the read head, use threshold strategy to enable/disable
   // deferring when the buffer is full/depleted.
   loader_->UpdateDeferStrategy(BufferedResourceLoader::kCapacityDefer);
 }
 
 }  // namespace media