Update ChannelReader to use AttachmentBroker.

ipc/attachment_broker_win.cc

 // Copyright 2015 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 "ipc/attachment_broker_win.h"
 
 #include "base/process/process.h"
 #include "ipc/attachment_broker_messages.h"
 #include "ipc/brokerable_attachment.h"
 #include "ipc/handle_attachment_win.h"
@@ skipping 23 matching lines @@
       internal::HandleAttachmentWin::WireFormat format =
           handle_attachment->GetWireFormat(destination_process);
       return sender_->Send(
           new AttachmentBrokerMsg_DuplicateWinHandle(format));
   }
   return false;
 }
 
 bool AttachmentBrokerWin::GetAttachmentWithId(
     BrokerableAttachment::AttachmentId id,
-    BrokerableAttachment* attachment) {
-  // TODO(erikchen): Implement me. http://crbug.com/493414
+    scoped_refptr<BrokerableAttachment>* out_attachment) {
+  for (AttachmentVector::iterator it = attachments_.begin();
+       it != attachments_.end(); ++it) {
+    if ((*it)->GetIdentifier() == id) {
+      *out_attachment = *it;
+      attachments_.erase(it);
+      return true;
+    }
+  }
   return false;
 }
 
 bool AttachmentBrokerWin::OnMessageReceived(const Message& msg) {
   bool handled = true;
   IPC_BEGIN_MESSAGE_MAP(AttachmentBrokerWin, msg)
     IPC_MESSAGE_HANDLER(AttachmentBrokerMsg_WinHandleHasBeenDuplicated,
                         OnWinHandleHasBeenDuplicated)
     IPC_MESSAGE_UNHANDLED(handled = false)
   IPC_END_MESSAGE_MAP()
   return handled;
 }
 
 void AttachmentBrokerWin::OnWinHandleHasBeenDuplicated(
     const IPC::internal::HandleAttachmentWin::WireFormat& wire_format) {
   // The IPC message was intended for a different process. Ignore it.
   if (wire_format.destination_process != base::Process::Current().Pid())
     return;
 
   scoped_refptr<BrokerableAttachment> attachment(
       new IPC::internal::HandleAttachmentWin(wire_format));
   attachments_.push_back(attachment);
+  NotifyObservers(attachment->GetIdentifier());
 }
 
 }  // namespace IPC