Add support for cancellation of demuxer reads.

chrome/utility/media_galleries/ipc_data_source.cc

 // Copyright 2014 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 "chrome/utility/media_galleries/ipc_data_source.h"
 
 #include "base/threading/thread_task_runner_handle.h"
 #include "chrome/common/extensions/chrome_utility_extensions_messages.h"
 #include "content/public/utility/utility_thread.h"
 
 namespace metadata {
 
 IPCDataSource::IPCDataSource(int64_t total_size)
     : total_size_(total_size),
       utility_task_runner_(base::ThreadTaskRunnerHandle::Get()),
       next_request_id_(0) {
   data_source_thread_checker_.DetachFromThread();
 }
 
 IPCDataSource::~IPCDataSource() {
   DCHECK(utility_thread_checker_.CalledOnValidThread());
 }
 
 void IPCDataSource::Stop() {
   DCHECK(data_source_thread_checker_.CalledOnValidThread());
 }
 
+void IPCDataSource::Abort() {
+  DCHECK(data_source_thread_checker_.CalledOnValidThread());
+}
+
 void IPCDataSource::Read(int64_t position,
                          int size,
                          uint8_t* data,
                          const DataSource::ReadCB& read_cb) {
   DCHECK(data_source_thread_checker_.CalledOnValidThread());
   utility_task_runner_->PostTask(
       FROM_HERE,
       base::Bind(&IPCDataSource::ReadOnUtilityThread, base::Unretained(this),
                  position, size, data, read_cb));
 }
@@ skipping 66 matching lines @@
   if (it == pending_requests_.end())
     return;
 
   std::copy(bytes.begin(), bytes.end(), it->second.destination);
   it->second.callback.Run(bytes.size());
 
   pending_requests_.erase(it);
 }
 
 }  // namespace metadata