Adds a --deterministic-fetch flag to headless_shell

headless/public/util/deterministic_http_protocol_handler.h

Index: headless/public/util/deterministic_http_protocol_handler.h
diff --git a/headless/public/util/deterministic_http_protocol_handler.h b/headless/public/util/deterministic_http_protocol_handler.h
new file mode 100644
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+++ b/headless/public/util/deterministic_http_protocol_handler.h
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+// 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 "base/single_thread_task_runner.h"
+#include "net/url_request/url_request_job_factory.h"
+
+namespace net {
+class URLRequestContext;
+class URLRequestJobFactory;
+}  // namespace
+
+namespace headless {
+class DeterministicDispatcher;
+class HeadlessBrowserContext;
+
+// A deterministic protocol handler.  Requests made 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.
+  DeterministicHttpProtocolHandler(
+      DeterministicDispatcher* deterministic_dispatcher,
+      scoped_refptr<base::SingleThreadTaskRunner> io_task_runner);
+  ~DeterministicHttpProtocolHandler() override;
+
+  net::URLRequestJob* MaybeCreateJob(
+      net::URLRequest* request,
+      net::NetworkDelegate* network_delegate) const override;
+
+ private:
+  class NopGenericURLRequestJobDelegate;
+
+  DeterministicDispatcher* deterministic_dispatcher_;  // NOT OWNED.
+  scoped_refptr<base::SingleThreadTaskRunner> io_task_runner_;
+  std::unique_ptr<NopGenericURLRequestJobDelegate> nop_delegate_;
+
+  // |url_request_context_| and |url_request_job_factory_| are lazily created on
+  // the IO thread. The URLRequestContext is setup to bypass any user-specified
+  // protocol handlers including this one. This is necessary to actually fetch
+  // http resources.
+  mutable std::unique_ptr<net::URLRequestContext> url_request_context_;
+  mutable std::unique_ptr<net::URLRequestJobFactory> url_request_job_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(DeterministicHttpProtocolHandler);
+};
+
+}  // namespace headless
+
+#endif  // HEADLESS_PUBLIC_UTIL_DETERMINISTIC_HTTP_PROTOCOL_HANDLER_H_