Adds a --deterministic-fetch flag to headless_shell

headless/public/util/deterministic_http_protocol_handler.h

+// 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.
+
+#ifndef HEADLESS_PUBLIC_UTIL_DETERMINISTIC_HTTP_PROTOCOL_HANDLER_H_
+#define HEADLESS_PUBLIC_UTIL_DETERMINISTIC_HTTP_PROTOCOL_HANDLER_H_
+
+#include <memory>
+
+#include "net/url_request/url_request_job_factory.h"
+
+namespace net {
+class URLRequestContext;
+}  // namespace
+
+namespace headless {
+class DeterministicDispatcher;
+class HeadlessBrowserContext;
+
+// A deterministic protocol handler.  Requests make to this protocol handler
+// will return in order of creation, regardless of what order the network
+// returns them in.  This helps remove one large source of network related
+// non determinism at the cost of slower page loads.
+class DeterministicHttpProtocolHandler
+    : public net::URLRequestJobFactory::ProtocolHandler {
+ public:
+  // Note |deterministic_dispatcher| is expected to be shared across a number of
+  // protocol handlers, e.g. for http & https protocols.
+  explicit DeterministicHttpProtocolHandler(
+      DeterministicDispatcher* deterministic_dispatcher);
+  ~DeterministicHttpProtocolHandler() override;
+
+  net::URLRequestJob* MaybeCreateJob(
+      net::URLRequest* request,
+      net::NetworkDelegate* network_delegate) const override;
+
+  void set_browser_context(HeadlessBrowserContext* browser_context) {

[Sami, 2016/09/22 12:09:40]

I wonder if we could avoid the dependency on the browser context by calling
URLRequestJobManager::GetInstance()->CreateJob() from MaybeCreateJob() (and
making sure to not do that re-entrantly)?

Alternatively should we structure this so that it uses another
net::URLRequestJobFactory::ProtocolHandler to implement fetching so that you
could hook this up to your custom protocol handler too?

[alex clarke (OOO till 29th), 2016/09/23 13:29:21]

We can get the context from the request itself.

+    browser_context_ = browser_context;
+  }
+
+ private:
+  class NopGenericURLRequestJobDelegate;
+
+  DeterministicDispatcher* deterministic_dispatcher_;  // NOT OWNED.
+  HeadlessBrowserContext* browser_context_;            // NOT OWNED.
+  std::unique_ptr<NopGenericURLRequestJobDelegate> nop_delagate_;
+
+  DISALLOW_COPY_AND_ASSIGN(DeterministicHttpProtocolHandler);
+};
+
+}  // namespace headless
+
+#endif  // HEADLESS_PUBLIC_UTIL_DETERMINISTIC_HTTP_PROTOCOL_HANDLER_H_