Follow-up work after current set of CLs is submitted:
- Add test for migration on write error, when network handles are not suported.
- replace migration_pending_ with sockets_.size()
- error propagation up the stack from migration errors

- add a test to (i) cause write error with no new network, causing pause, (ii) new network gets added, but no new network notification, (iii) onnetworkdisconected issued, causing migration to finish, (iv) onnetworkconnected issued, which is a nop.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/9f3037153a2feb63bbaeaf07ab35c8ff9a3096ad

commit 9f3037153a2feb63bbaeaf07ab35c8ff9a3096ad
Author: jri <jri@chromium.org>
Date: Tue Sep 13 01:10:22 2016

This CL refactors the code for migration on write error, making it asynchronous to avoid reentrancyissues. Also simplifies some methods in QuicStreamFactory.

BUG= 646145 

Review-Url: https://codereview.chromium.org/2319343004
Cr-Commit-Position: refs/heads/master@{#418128}

[modify] https://crrev.com/9f3037153a2feb63bbaeaf07ab35c8ff9a3096ad/net/quic/chromium/mock_network_change_notifier.cc
[modify] https://crrev.com/9f3037153a2feb63bbaeaf07ab35c8ff9a3096ad/net/quic/chromium/mock_network_change_notifier.h
[modify] https://crrev.com/9f3037153a2feb63bbaeaf07ab35c8ff9a3096ad/net/quic/chromium/quic_chromium_client_session.cc
[modify] https://crrev.com/9f3037153a2feb63bbaeaf07ab35c8ff9a3096ad/net/quic/chromium/quic_chromium_client_session.h
[modify] https://crrev.com/9f3037153a2feb63bbaeaf07ab35c8ff9a3096ad/net/quic/chromium/quic_chromium_client_session_test.cc
[modify] https://crrev.com/9f3037153a2feb63bbaeaf07ab35c8ff9a3096ad/net/quic/chromium/quic_chromium_packet_writer.cc
[modify] https://crrev.com/9f3037153a2feb63bbaeaf07ab35c8ff9a3096ad/net/quic/chromium/quic_chromium_packet_writer.h
[modify] https://crrev.com/9f3037153a2feb63bbaeaf07ab35c8ff9a3096ad/net/quic/chromium/quic_stream_factory.cc
[modify] https://crrev.com/9f3037153a2feb63bbaeaf07ab35c8ff9a3096ad/net/quic/chromium/quic_stream_factory.h
[modify] https://crrev.com/9f3037153a2feb63bbaeaf07ab35c8ff9a3096ad/net/quic/chromium/quic_stream_factory_test.cc

#2 done.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e3d187c4260655a356b3685001458d0f9ec91102

commit e3d187c4260655a356b3685001458d0f9ec91102
Author: jri <jri@chromium.org>
Date: Fri Sep 16 14:29:17 2016

Fixes crash bug when iterating through sessions in OnNetworkConnected.

BUG= 646145 

Review-Url: https://codereview.chromium.org/2344053003
Cr-Commit-Position: refs/heads/master@{#419162}

[modify] https://crrev.com/e3d187c4260655a356b3685001458d0f9ec91102/net/quic/chromium/quic_stream_factory.cc
[modify] https://crrev.com/e3d187c4260655a356b3685001458d0f9ec91102/net/quic/chromium/quic_stream_factory_test.cc

Archiving as this bug was tracking connection migration v1, which is removed from chromium. And we are moving to Connection Migration V2 as of today and consistently working on the improvements. Please see https://bugs.chromium.org/p/chromium/issues/detail?id=818259 for more details.