Add reprioritization to socket pools.

net/http/http_network_transaction.cc

 // Copyright (c) 2012 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.
 
 #include "net/http/http_network_transaction.h"
 
 #include <memory>
 #include <set>
 #include <utility>
 #include <vector>
@@ skipping 403 matching lines @@
 void HttpNetworkTransaction::PopulateNetErrorDetails(
     NetErrorDetails* details) const {
   *details = net_error_details_;
   if (stream_)
     stream_->PopulateNetErrorDetails(details);
 }
 
 void HttpNetworkTransaction::SetPriority(RequestPriority priority) {
   priority_ = priority;
 
-  // TODO: Note that if throttling is ever implemented below this
-  // level, either of the two below calls may result in request
-  // completion, callbacks, and the potential deletion of this object
-  // (like the call below to throttle_->SetPriority()).  In that case,
-  // this code will need to be modified.
+  // TODO(rdsmith): Note also that if priority-based throttling is
+  // ever implemented below this level, either of the two below calls
+  // may result in request completion, callbacks, and the potential
+  // deletion of this object (like the call below to
+  // throttle_->SetPriority()).  In that case, this code will need to
+  // be modified.

[mmenke, 2017/01/05 20:18:35]

Ok, now I understand what you mean because of your response to me, but I still
think the socket pools implement priority-based throttling.  Once the pool limit
is reached, the group with the highest priority open socket request gets the
next socket slot.

Maybe be more explicit:  "Note that if any level below this ever implements a
throttling mechanism where changing a request's priority may cause *any* request
to synchronously succeed or fail, that callback could synchronously delete
|this|, and this code could potentially crash.  In that case, this code will
need to be modified."

[Randy Smith (Not in Mondays), 2017/01/13 23:05:44]

Done, though I felt a need to be a bit wordier once I got going.  Let me know
what you think.

   if (stream_request_)
     stream_request_->SetPriority(priority);
   if (stream_)
     stream_->SetPriority(priority);
 
   if (throttle_)
     throttle_->SetPriority(priority);
   // The above call may have resulted in deleting |*this|.
 }
 
@@ skipping 1261 matching lines @@
   DCHECK(stream_request_);
 
   // Since the transaction can restart with auth credentials, it may create a
   // stream more than once. Accumulate all of the connection attempts across
   // those streams by appending them to the vector:
   for (const auto& attempt : stream_request_->connection_attempts())
     connection_attempts_.push_back(attempt);
 }
 
 }  // namespace net