Add reprioritization to socket pools.

net/http/http_stream_factory_impl_job.cc

Index: net/http/http_stream_factory_impl_job.cc
diff --git a/net/http/http_stream_factory_impl_job.cc b/net/http/http_stream_factory_impl_job.cc
index 375a71b9d3c5d208a7f573674fb410f542ac1141..5b3c5cd8515c86acdf02881cd12bd8fee48ad2ae 100644
--- a/net/http/http_stream_factory_impl_job.cc
+++ b/net/http/http_stream_factory_impl_job.cc
@@ -318,8 +318,12 @@ void HttpStreamFactoryImpl::Job::Orphan() {
 
 void HttpStreamFactoryImpl::Job::SetPriority(RequestPriority priority) {
   priority_ = priority;
-  // TODO(akalin): Propagate this to |connection_| and maybe the
-  // preconnect state.
+  // connection_ is moved to be owned by the newly created stream

[mmenke, 2017/01/03 22:51:22]

"connection_ is moved to be owned by the newly created stream..." -> Maybe
"Ownership of |connection_| is passed to the newly created stream or H2 session
in DoCreateStream(), and the consumer not notified immediately, so this call may
occur when connection_ is null."

[mmenke, 2017/01/03 22:51:22]

Also, would it make more sense to put the TODO about fixing that case here?  I
think all you need to do (Excluding tests) to fix that is:

if (stream_)
  stream_->SetPriority(priority);

[Randy Smith (Not in Mondays), 2017/01/05 03:47:18]

Huh; I had thought the PostTask() went to an object method above this one, but
it's actually just to OnStreamReadyCallback().  Yes, I think that would work
fine, and I think it's a better API contract (i.e. that the consumer should
always be able to affect the priority via one of stream_request_ or stream_).  

Do you see any way to test it?  There aren't currently any
HttpStreamFactoryImpl::Job unit tests, which I think I could make work; without
that (specifically without notification of connection establishment separate
from stream ready) I don't know how to get into the state where the PostTask is
in flight.

Failing seeing how to test it (relatively easily--this CL is a distraction from
my main tasks ATM) I've moved the TODO.

[Randy Smith (Not in Mondays), 2017/01/05 03:47:18]

Done.

+  // (or equivalent) in DoCreateStream(), and the consumer not notified
+  // until after a PostTask, so this call may occur when connection_ is null.
+  if (connection_)
+    connection_->SetPriority(priority);
+  // TODO(akalin): Maybe Propagate this to the preconnect state.
 }
 
 bool HttpStreamFactoryImpl::Job::was_alpn_negotiated() const {