Add support in the network service for different contexts.

content/browser/url_loader_factory_getter.cc

+// 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.
+
+#include "content/browser/url_loader_factory_getter.h"
+
+#include "base/bind.h"
+
+namespace content {
+
+URLLoaderFactoryGetter::URLLoaderFactoryGetter() {}
+
+URLLoaderFactoryGetter::~URLLoaderFactoryGetter() {}
+
+void URLLoaderFactoryGetter::Initialize(
+    mojom::URLLoaderFactoryPtr network_factory) {
+  BrowserThread::PostTask(
+      BrowserThread::IO, FROM_HERE,
+      base::BindOnce(&URLLoaderFactoryGetter::InitializeOnIOThread, this,
+                     std::move(network_factory.PassInterface())));
+}
+
+mojom::URLLoaderFactoryPtr* URLLoaderFactoryGetter::GetNetworkFactory() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));

[scottmg, 2017/05/16 03:53:43]

DCHECK_CURRENTLY_ON(BrowserThread::IO);

[jam, 2017/05/16 04:08:40]

Done.

+  return test_factory_.is_bound() ? &test_factory_ : &network_factory_;
+}
+
+void URLLoaderFactoryGetter::SetNetworkFactoryForTesting(
+    mojom::URLLoaderFactoryPtr test_factory) {
+  // Since the URLLoaderFactory pointers are bound on the IO thread, and this
+  // method is called on the UI thread, we are not able to unbind and return the
+  // old value. As such this class keeps two separate pointers, one for test.
+  BrowserThread::PostTask(

[scottmg, 2017/05/16 03:53:43]

I was worried at first about this racing with the subsequent call to the user of
the test factory, but I guess since we necessarily navigate on UI, and call
GetNetworkFactory() which DCHECKs that it's on IO, it's pretty future-safe.

[jam, 2017/05/16 04:08:40]

Yep exactly :)

+      BrowserThread::IO, FROM_HERE,
+      base::BindOnce(&URLLoaderFactoryGetter::SetTestNetworkFactoryOnIOThread,
+                     this, std::move(test_factory.PassInterface())));
+}
+
+void URLLoaderFactoryGetter::InitializeOnIOThread(
+    mojom::URLLoaderFactoryPtrInfo network_factory) {
+  network_factory_.Bind(std::move(network_factory));
+}
+
+void URLLoaderFactoryGetter::SetTestNetworkFactoryOnIOThread(
+    mojom::URLLoaderFactoryPtrInfo test_factory) {
+  test_factory_.Bind(std::move(test_factory));
+}
+
+}  // namespace content