[NetInfo] Browser changes to support connection.downlinkMax

Patch 1) https://crrev.com/1308943005
Patch 2) https://crrev.com/1306423004 (this)
Patch 3) https://crrev.com/1309903006

Also depends on https://codereview.chromium.org/1306653003/

BUG=412741

Review URL: https://codereview.chromium.org/1306423004

Cr-Commit-Position: refs/heads/master@{#349739}
15 files changed