Hook up ProfileIOData's URLRequestContext to a NetworkService.

chrome/browser/net/profile_network_context_service.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_PROFILE_NETWORK_CONTEXT_SERVICE_H_
+#define CHROME_BROWSER_NET_PROFILE_NETWORK_CONTEXT_SERVICE_H_
+
+#include "base/macros.h"
+#include "components/keyed_service/core/keyed_service.h"
+#include "content/public/common/network_service.mojom.h"
+
+class Profile;
+
+// KeyedService that initializes and provides access to the NetworkContexts for
+// a Profile. This will eventually replace ProfileIOData.
+class ProfileNetworkContextService : public KeyedService {
+ public:
+  explicit ProfileNetworkContextService(Profile* profile);
+  ~ProfileNetworkContextService() override;
+
+  // Initializes |network_context_params| as needed to set up the
+  // ProfileIOData's main URLRequestContext (Which the caller will need to send
+  // to the IOThread's in-process NetworkService). If the network service is
+  // disabled, this will be the NetworkContext returned by the MainContext()
+  // method, and used by all the requests associated with a profile. If the
+  // network service is enabled, this method is still used, but only legacy
+  // requests going through the URLRequestContext interface instead of the
+  // NetworkContext interface will use the ProfileIOData's URLRequestContext,
+  // and the ProfileIOData's main URLRequestContext will be configured not to
+  // use on-disk storage, as the network service will be using those files
+  // instead.

[Randy Smith (Not in Mondays), 2017/07/20 17:38:34]

Ok, I do find this clearer.  It's still somewhat hard going for me, but I'm not
sure if that's a failure of comprehension on my part, or documentation changes
would be useful in general.  So the following are suggestions, take them or not
as you wish.

* Change the first sentence to mention network_context_request.  

* Add after that sentence something that makes explicit that
|*network_context_request| is one end of a pipe and the class is retaining the
other end.

* Change the "If the network service is enabled" sentence to be parallel in
structure with the disabled sentence. 

I envision something like:

----
Initializes |*network_context_params| as needed to set up the ProfileIOData's
main URLRequestContext and |*network_context_request| as one end of a Mojo pipe
to be bound to the NetworkContext for that URLRequestContext.  (The caller will
need to send these parameters to the IOThread's in-process NetworkService.) .
The class retains the other end of the |*network_context_request| pipe for later
vending.

If the network service is disabled, MainContext() will return that end of the
pipe.  In this case, all requests associated with this profile will use the
associated URLRequestContext (either through MainContext() or directly).  

If the network service is enabled, MainContext() will instead return a network
context vended by the NetworkService.  In this case, the ProfileIOData's
URLRequest context will be configured not to use on-disk storage (so as not to
conflict with the NetworkService vended context), and will only be used for
legacy requests.  

Must be called before the system NetworkContext is first used.
---

but up to you.

[mmenke, 2017/07/20 18:31:30]

Thanks so much for the detailed text - I think it's a lot better, and have
switched to it (With a minor change or two).

+  //
+  // Must be called before the system NetworkContext is first used.
+  void SetUpProfileIODataMainContext(
+      content::mojom::NetworkContextRequest* network_context_request,
+      content::mojom::NetworkContextParamsPtr* network_context_params);
+
+  // Returns the main NetworkContext for the BrowserContext.

[Randy Smith (Not in Mondays), 2017/07/20 17:38:34]

suggestion: Add "If the network service is disabled, this will be the
ProfileIOData NetworkContext setup above.  Otherwise, it will be a
NetworkContext vended from the network service."

[mmenke, 2017/07/20 18:31:30]

Done.

+  content::mojom::NetworkContext* MainContext();
+
+  // Creates the main NetworkContext for the BrowserContext. May only be called

[Randy Smith (Not in Mondays), 2017/07/20 17:38:34]

Suggest adding to first sentence ", by requesting it from the network service."

[mmenke, 2017/07/20 18:31:30]

Done (Added "using the network service", "requesting" has a bit of an
implication of requesting something that already exists)

+  // when the network service is enabled. Must only be called once for a
+  // profile, from the ChromeContentBrowserClient.
+  content::mojom::NetworkContextPtr CreateMainNetworkContext();
+
+ private:
+  Profile* const profile_;
+
+  // This is a NetworkContext that wraps ProfileIOData's main URLRequestContext.
+  // Always initialized in SetUpProfileIODataMainContext, but it's only returned
+  // by Context() when the network service is disabled.
+  content::mojom::NetworkContextPtr profile_io_data_main_network_context_;
+
+  DISALLOW_COPY_AND_ASSIGN(ProfileNetworkContextService);
+};
+
+#endif  // CHROME_BROWSER_NET_PROFILE_NETWORK_CONTEXT_SERVICE_H_