Add virtual tests for XHR with mojo-loading

content/child/url_response_body_consumer.cc

 // Copyright 2016 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 "content/child/url_response_body_consumer.h"
 
 #include "base/bind.h"
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "content/child/resource_dispatcher.h"
@@ skipping 69 matching lines @@
 
 void URLResponseBodyConsumer::Reclaim(uint32_t size) {
   MojoResult result = mojo::EndReadDataRaw(handle_.get(), size);
   DCHECK_EQ(MOJO_RESULT_OK, result);
 }
 
 void URLResponseBodyConsumer::OnReadable(MojoResult unused) {
   if (has_been_cancelled_ || has_seen_end_of_data_)
     return;
 
+  // Protect |this| as RequestPeer::OnReceivedData may call deref.
+  scoped_refptr<URLResponseBodyConsumer> protect(this);

[nasko, 2016/11/08 01:12:12]

What causes the OnReceivedData to ref-count down this object? Is it a failure
condition? Is this code safe in face of such condition?

[yhirano, 2016/11/08 01:34:45]

RequestPeer::OnReceivedData may cancel the request. The cancel operation 

 1. calls URLResponseBodyConsumer::Cancel, and
 2. dereferences the URLResponseBodyConsumer.

Without this scoped_refptr, |this| URLResponseBodyConsumer will be destructed at
that time. With this scoped_refptr, this function will return because
has_been_cancelled_ will be set when URLResponseBodyConsumer::Cancel is called.

[nasko, 2016/11/08 16:32:15]

I was missing the bit about has_been_cancelled_ being set to true in the
::Cancel method. Thanks for the details!

+
   // TODO(yhirano): Suppress notification when deferred.
   while (!has_been_cancelled_) {
     const void* buffer = nullptr;
     uint32_t available = 0;
     MojoResult result = mojo::BeginReadDataRaw(
         handle_.get(), &buffer, &available, MOJO_READ_DATA_FLAG_NONE);
     if (result == MOJO_RESULT_SHOULD_WAIT)
       return;
     if (result == MOJO_RESULT_FAILED_PRECONDITION) {
       has_seen_end_of_data_ = true;
@@ skipping 22 matching lines @@
     return;
   // Cancel this instance in order not to notify twice.
   Cancel();
 
   resource_dispatcher_->OnMessageReceived(
       ResourceMsg_RequestComplete(request_id_, completion_status_));
   // |this| may be deleted.
 }
 
 }  // namespace content