Initial implementation of RequestPriority-based HTTP/2 dependencies.

net/spdy/spdy_session.h

Index: net/spdy/spdy_session.h
diff --git a/net/spdy/spdy_session.h b/net/spdy/spdy_session.h
index 3ad5d27138d980b3d2adf9fab5cf5d73d6bbb3ce..a18aefc70323cfa1dd9d96bb5d3e219a1db2b0e4 100644
--- a/net/spdy/spdy_session.h
+++ b/net/spdy/spdy_session.h
@@ -516,6 +516,10 @@ class NET_EXPORT SpdySession : public BufferedSpdyFramerVisitorInterface,
   // HigherLayeredPool implementation:
   bool CloseOneIdleConnection() override;
 
+  // Set whether priority->dependency conversion is enabled
+  // by default for all future SpdySessions.
+  static void SetPriorityDependencyDefaultForTesting(bool enable);

[Bence, 2015/11/11 18:47:15]

I don't like the idea of having a global variable for this, but I see that there
is no easy way around it.

I don't like the idea of making this method public, and if every test file
already had a peer class, I would propose to friend those peer classes here and
make this method private, but they don't, and it would be unreasonable to create
them just for this.

Maybe "ForTesting" in the method name is enough to deter developers from calling
it in non-test code.

[Randy Smith (Not in Mondays), 2015/11/11 23:25:59]

Agreed.
I'm not sure what you mean by peer class?  I added a mess of "friends" and
shifted around some anonymous namespaces, and got this method private; does that
do what you wanted?

+
  private:
   friend class base::RefCounted<SpdySession>;
   friend class SpdyStreamRequest;
@@ -1004,6 +1008,14 @@ class NET_EXPORT SpdySession : public BufferedSpdyFramerVisitorInterface,
   // them?
   ActiveStreamMap active_streams_;
 
+  // Per-priority map from stream id to all active streams.  This map will
+  // contain the same set of streams as |active_streams_|.  It is used for
+  // setting dependencies to match incoming requests RequestPriority.
+  //
+  // |active_streams_by_priority_| does *not* own its SpdyStream objects.
+  std::map<SpdyStreamId, SpdyStream*>
+      active_streams_by_priority_[NUM_PRIORITIES];
+
   // (Bijective) map from the URL to the ID of the streams that have
   // already started to be pushed by the server, but do not have
   // consumers yet. Contains a subset of |active_streams_|.
@@ -1182,6 +1194,10 @@ class NET_EXPORT SpdySession : public BufferedSpdyFramerVisitorInterface,
 
   TimeFunc time_func_;
 
+  // Should priority-based depencency information be sent in stream header

[Bence, 2015/11/11 18:47:15]

s/depencency/dependency/

[Randy Smith (Not in Mondays), 2015/11/11 23:25:59]

Done.

+  // frames.
+  bool send_priority_dependency_;
+
   // Used for posting asynchronous IO tasks.  We use this even though
   // SpdySession is refcounted because we don't need to keep the SpdySession
   // alive if the last reference is within a RunnableMethod.  Just revoke the