Introduce SystemNetworkContextManager.

chrome/browser/net/system_network_context_manager.h

+// Copyright 2017 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.
+
+#ifndef CHROME_BROWSER_NET_SYSTEM_NETWORK_CONTEXT_MANAGER_H_
+#define CHROME_BROWSER_NET_SYSTEM_NETWORK_CONTEXT_MANAGER_H_
+
+#include <memory>
+
+#include "base/lazy_instance.h"
+#include "base/macros.h"
+#include "content/public/common/network_service.mojom.h"
+
+// Global object that lives on the UI thread. Responsible for creating and
+// managing access to the system NetworkContext. This NetworkContext is intended
+// for requests not associated with a profile. It stores no data on disk, and
+// has no HTTP cache, but it does have ephemeral cookie and channel ID stores.
+// It also does not have access to HTTP proxy auth information the user has
+// entered or that comes from extensions, and similarly, has no
+// extension-provided per-profile proxy configuration information.
+//
+// The "system" NetworkContext will either share a URLRequestContext with
+// IOThread's SystemURLRequestContext and be part of IOThread's NetworkService
+// (If the network service is disabled) or be an independent NetworkContext
+// using the actual network service.
+//
+// This class is intended to eventually replace IOThread. Handling the two cases
+// differently allows this to be used in production without breaking anything or
+// requiring two separate paths, while IOThread consumers slowly transition over
+// to being compatible with the network service.
+class SystemNetworkContextManager {
+ public:
+  // Initializes |network_context_params| as needed to set up a system
+  // NetworkContext. If the network service is disabled,
+  // |network_context_request| will be for the NetworkContext used by the
+  // SystemNetworkContextManager. Otherwise, this method can still be used to
+  // help set up the IOThread's in-process URLRequestContext, and
+  // |network_context_request| will still be populated, but the associated
+  // NetworkContext will not be used by the SystemNetworkContextManager.
+  //
+  // Must be called before the system NetworkContext is first used.
+  static void SetUp(
+      content::mojom::NetworkContextRequest* network_context_request,
+      content::mojom::NetworkContextParamsPtr* network_context_params);
+
+  // Returns the System NetworkContext. May only be called after SetUp().
+  static content::mojom::NetworkContext* Context();
+
+ private:
+  static SystemNetworkContextManager* GetInstance();
+
+  friend struct base::LazyInstanceTraitsBase<SystemNetworkContextManager>;
+
+  SystemNetworkContextManager();
+  ~SystemNetworkContextManager();
+
+  // Gets the system NetworkContext, creating it if needed.
+  content::mojom::NetworkContext* GetContext();
+
+  // The NetworkContext used by the |SystemNetworkContextManager|. If the
+  // network service is enabled, it's a NetworkContext using that
+  // NetworkService. If it's not enabled, it's a NetworkContext wrapping the
+  // IOThread's SystemURLRequestContext.

[asanka, 2017/07/13 01:52:29]

The fact that system_network_context_ is bound to the IOThread's network context
while io_thread_network_context_ is nil was quite confusing to me.

It would've been easier to understand if io_thread_network_context_ is
unconditionally wrapping the IOThread's NetworkContext and have
SystemNetworkContextManager::Context() bind via the out-of-process network
service depending on the feature state. That way we can call this
out_of_process_network_context_ or something.

Also is it possible to bind out_of_process_network_context_ at
SystemNetworkContextManager::SetUp()? If so SetUp() can return the
NetworkContextRequest for io_thread_network_context_ and, if the feature is
enabled, bind out_of_process_network_context_. This way
SystemNetworkContextManager::GetContext() is ready to fire without fiddling with
bindings.

[mmenke, 2017/07/13 16:15:18]

Done.  I called it the network_service_network_context_, though.
I tried this initially.  Unfortunately, the service manager is set up after the
IOThread is.

+  content::mojom::NetworkContextPtr system_network_context_;
+
+  // When the network service is enabled, this is a NetworkContext that wraps
+  // the IOThread's SystemURLRequestContext, and is never used after
+  // initialization. It's nullptr, otherwise.
+  content::mojom::NetworkContextPtr io_thread_network_context_;
+
+  DISALLOW_COPY_AND_ASSIGN(SystemNetworkContextManager);
+};
+
+#endif  // CHROME_BROWSER_NET_SYSTEM_NETWORK_CONTEXT_MANAGER_H_