Fix bug in net::RequestPriority -> HTTP/2 dependency conversion.

net/spdy/http2_priority_dependencies.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 NET_HTTP2_PRIORITY_DEPENDENCIES_H_
+#define NET_HTTP2_PRIORITY_DEPENDENCIES_H_
+
+#include <list>
+#include <map>
+
+#include "net/base/request_priority.h"
+#include "net/spdy/spdy_protocol.h"
+
+namespace net {
+
+// A helper class encapsulating the state and logic to set dependencies of
+// HTTP2 streams based on their net::RequestPriority and the ordering
+// of creation and deletion of the streams.
+class Http2PriorityDependencies {
+ public:
+  Http2PriorityDependencies();
+  ~Http2PriorityDependencies();
+
+  // Called to override default behavior for testing.  If |enabled|,
+  // |OnStreamSynSent()| will output correct header values; if
+  // |!enabled|, |*dependent_stream_id| will be set to 0 and
+  // |*exclusive| to false.
+  // Returns old default value (for resetting at end of test).
+  static bool SetEnabledDefaultForTesting(bool enabled);
+
+  // Called when a stream SYN is sent to the server.  Note that in the
+  // case of server push, a stream may be created without this routine
+  // being called.  In such cases, the client ignores the stream's priority
+  // (as the server is effectively overriding the client's notions of
+  // priority anyway.

[Bence, 2016/03/10 20:21:14]

Nit: close opening parenthesis.

[Randy Smith (Not in Mondays), 2016/03/16 19:38:10]

Done.

+  // On return, |*dependent_stream_id| is set to the stream id that
+  // this stream should be made dependent on, and |*exclusive| set to
+  // whether that dependency should be exclusive.
+  void OnStreamSynSent(SpdyStreamId id,
+                       RequestPriority priority,
+                       SpdyStreamId* dependent_stream_id,
+                       bool* exclusive);
+
+  void OnStreamDestruction(SpdyStreamId id);
+
+ private:
+  bool enabled_;
+
+  // The requirements for the internal data structure for this class are:
+  //     a) Constant time insertion of entries at the end of the list,
+  //     b) Fast removal of any entry based on its id.
+  //     c) Constant time lookup of the entry at the end of the list.
+  // std::list would satisfy (a) & (c), but some form of map is
+  // needed for (b).  The priority must be included in the map
+  // entries so that deletion can determine which list in id_priority_lists_
+  // to erase from.

[Bence, 2016/03/10 20:21:14]

Makes sense.  Too bad you have multiple lists and thus cannot use
linked_hash_map.

[Randy Smith (Not in Mondays), 2016/03/16 19:38:10]

Acknowledged.

+  using IdList = std::list<std::pair<SpdyStreamId, net::RequestPriority>>;
+  using EntryMap = std::map<SpdyStreamId, IdList::iterator>;
+
+  IdList id_priority_lists_[NUM_PRIORITIES];
+
+  // Tracks the location of an id anywhere in the above vector of lists.
+  // Iterators to list elements remain valid until those particular elements
+  // are erased.
+  EntryMap entry_by_stream_id_;
+};
+
+}  // namespace net
+
+#endif  // NET_HTTP2_PRIORITY_DEPENDENCIES_H_