Add a member variable in QuicStreamFactory to track the current default network.

Also add a histogram to collect data on how often initial sockets are created on a different network than the one QuicStreamFactory marks.

Bug: 790547
Change-Id: I630f31fd3f934aa6617935cdc3b13623337dd08a
Reviewed-on: https://chromium-review.googlesource.com/1063114
Reviewed-by: Ryan Hamilton <[email protected]>
Reviewed-by: Steven Holte <[email protected]>
Commit-Queue: Zhongyi Shi <[email protected]>
Cr-Commit-Position: refs/heads/master@{#560136}
3 files changed