[Temp] Backport r21402 from the bleeding_edge branch.

Original commit message:

> Stop using urllib.urlretrieve() directly.
>
> Using urllib for SSL connections when behind a proxy is known to be
> broken, so apply the same fix from depot_tools r149742 and use a wrapper
> around urllib2 instead.
>
> R=jkummerow@chromium.org
> TEST=run test262 behind corporate proxy
>
> Review URL: https://codereview.chromium.org/297663003
>
> Patch from Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>.

This is necessary for the test262 tests to pass inside the network our
v8-crosswalk bots run in.