Add a header when fetching pages under the DMServer URL.

components/policy/core/browser/policy_header_io_helper.h

Index: components/policy/core/browser/policy_header_io_helper.h
diff --git a/components/policy/core/browser/policy_header_io_helper.h b/components/policy/core/browser/policy_header_io_helper.h
new file mode 100644
index 0000000000000000000000000000000000000000..fa1f7b145dee0b6d1c84aa055404865674cce3f0
--- /dev/null
+++ b/components/policy/core/browser/policy_header_io_helper.h
@@ -0,0 +1,63 @@
+// Copyright (c) 2013 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 COMPONENTS_POLICY_CORE_BROWSER_POLICY_HEADER_IO_HELPER_H_
+#define COMPONENTS_POLICY_CORE_BROWSER_POLICY_HEADER_IO_HELPER_H_
+
+#include <string>
+
+#include "base/memory/ref_counted.h"
+#include "base/memory/weak_ptr.h"
+#include "base/sequenced_task_runner.h"
+#include "components/policy/policy_export.h"
+
+namespace net {
+class URLRequest;
+}
+
+namespace policy {
+
+// Helper class that lives on the I/O thread and adds policy headers to
+// outgoing requests. Instances of this class are created by
+// PolicyHeaderService on the UI thread, and that class is responsible for
+// notifying this class via UpdateHeaderFromUI() when the header changes.
+// Ownership is transferred to ProfileIOData, and this object is run and
+// destroyed on the I/O thread.
+class POLICY_EXPORT PolicyHeaderIOHelper {
+ public:
+  PolicyHeaderIOHelper(const std::string& server_url,
+                       const std::string& initial_header_value,
+                       scoped_refptr<base::SequencedTaskRunner> task_runner);

[willchan no longer on Chromium, 2013/12/10 23:27:09]

const reference to eliminate the extra copy for the scoped_refptr?

[Andrew T Wilson (Slow), 2013/12/10 23:53:06]

OK, I didn't think the cost of creating the scoped_refptr was a big deal, but
I've changed it as you suggest.

[willchan no longer on Chromium, 2013/12/10 23:55:20]

Just one of those death by a thousand cut things. Especially for ARM devices
since atomics are more expensive there (this uses an atomic increment/decrement
pair for the threadsafe refcounted objects).

+  ~PolicyHeaderIOHelper();
+
+  // Sets any necessary policy headers on the passed request. Should be invoked
+  // only from the I/O thread.
+  void AddPolicyHeaders(net::URLRequest* request) const;
+
+  // API invoked when the header changes. Can be called from any thread - calls
+  // are marshalled via the TaskRunner to run on the appropriate thread.
+  // If |new_header| is the empty string, no header will be added to
+  // outgoing requests.
+  void UpdateHeader(const std::string& new_header);
+
+ private:
+  // API invoked via the TaskRunner to update the header.
+  void UpdateHeaderOnTaskRunner(const std::string& new_header);
+
+  // The URL we should add policy headers to.
+  std::string server_url_;
+
+  // The task runner assocated with the thread that runs this object.
+  scoped_refptr<base::SequencedTaskRunner> task_runner_;
+
+  // The current policy header value.
+  std::string policy_header_;
+
+  base::WeakPtrFactory<PolicyHeaderIOHelper> weak_factory_;
+  DISALLOW_COPY_AND_ASSIGN(PolicyHeaderIOHelper);
+};
+
+}  // namespace policy
+
+#endif  // COMPONENTS_POLICY_CORE_BROWSER_POLICY_HEADER_IO_HELPER_H_