Use a utility process for the Mojo v8 proxy resolver.

chrome/browser/net/utility_process_mojo_proxy_resolver_factory.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 "chrome/browser/net/utility_process_mojo_proxy_resolver_factory.h"
+
+#include "base/logging.h"
+#include "base/memory/singleton.h"
+#include "content/public/browser/browser_thread.h"
+#include "content/public/browser/utility_process_host.h"
+#include "content/public/browser/utility_process_host_client.h"
+#include "content/public/common/service_registry.h"
+#include "net/proxy/mojo_proxy_resolver_factory.h"
+
+namespace chrome_browser_net {
+
+// static
+UtilityProcessMojoProxyResolverFactory*
+UtilityProcessMojoProxyResolverFactory::GetInstance() {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
+  return Singleton<
+      UtilityProcessMojoProxyResolverFactory,
+      LeakySingletonTraits<UtilityProcessMojoProxyResolverFactory>>::get();
+}
+
+UtilityProcessMojoProxyResolverFactory::
+    UtilityProcessMojoProxyResolverFactory() {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
+}
+
+UtilityProcessMojoProxyResolverFactory::
+    ~UtilityProcessMojoProxyResolverFactory() {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
+}
+
+void UtilityProcessMojoProxyResolverFactory::CreateProcessAndConnect() {
+  DVLOG(1) << "Attempting to create utility process for proxy resolver";
+  content::UtilityProcessHost* utility_process_host =
+      content::UtilityProcessHost::Create(

[eroman, 2015/03/06 05:48:21]

What is the lifetime of this process? It seems like the first time it is
created, it will keep on living ad-infinitum, is that correct?

Proxy configurations however are dynamic, and if PAC is no longer being used
this process should be released.

This may need some refactoring to get the right signal though, since IIRC
ProxyResolver is always alive even when not in use.

[Anand Mistry (off Chromium), 2015/03/10 07:24:23]

Yes, for now. For other Mojo services, I'm planning on using the utility process
reference counting to control the life cycle. But that's not going to work for
the proxy resolver.
This is something I'm still thinking about. We need two things:
1. Signal that the ProxyResolver is not being used.
2. Shut down the utility process when there are 0 services active (since we use
the same service for all resolvers for all users).

If it's ok with you, I'd like to punt the issue of utility process life cycle to
the "fix this before enabling by default" list. I know it's fundamental, but
it'll be easier to review the changes separately and I'd like to get some usage
for this as soon as possible so we can iron out other issues in parallel.

[eroman, 2015/03/11 18:48:35]

One way we could solve this is to make ProxyService have a dependency on a
ProxyResolverFactory rather than a ProxyResolver.

ProxyService would then create and destroy the ProxyResolver to reflect when it
is being used (and perhaps SetPacScript could be moved to part of the creation
parameters rather than a stateful method).

Then the reference counting approach would work since ProxyResolver being alive
would also correspond with it being actively needed.

+          scoped_refptr<content::UtilityProcessHostClient>(),
+          base::MessageLoopProxy::current().get());
+  bool process_started = utility_process_host->StartMojoMode();
+  if (process_started) {
+    content::ServiceRegistry* service_registry =
+        utility_process_host->GetServiceRegistry();
+    service_registry->ConnectToRemoteService(&resolver_factory_);
+    resolver_factory_.set_error_handler(this);
+  } else {
+    LOG(ERROR) << "Unable to connect to utility process";
+  }
+}
+
+void UtilityProcessMojoProxyResolverFactory::Create(
+    mojo::InterfaceRequest<net::interfaces::ProxyResolver> req,
+    net::interfaces::HostResolverPtr host_resolver) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
+  if (!resolver_factory_)
+    CreateProcessAndConnect();
+
+  if (!resolver_factory_) {
+    // If there's still no factory, then utility process creation failed so
+    // close |req|'s message pipe, which should cause a connection error.
+    req = nullptr;
+    return;
+  }
+  resolver_factory_->CreateResolver(req.Pass(), host_resolver.Pass());
+}
+
+void UtilityProcessMojoProxyResolverFactory::OnConnectionError() {
+  DVLOG(1) << "Disconnection from utility process detected";
+  resolver_factory_.reset();
+}
+
+}  // namespace chrome_browser_net