Work around issues w/ https_proxy causing webkitpy autoinstaller to fail.

It looks like for some reason urllib checks 'https_proxy' in the environment,
but not 'HTTPS_PROXY', and this is causing an issue on some of the GCE-based
bots. We can fix this on the bots (by setting both values) but that will
require master restarts and fleet-wide slave restarts. Instead, I'll fix
this in the code temporarily.

A better long-term fix is to just check in the third-party libs and get rid
of the autoinstaller and the dependencies.

TBR=ojan@chromium.org
BUG=230706
NOTRY=1

Review URL: https://codereview.chromium.org/18661008

git-svn-id: svn://svn.chromium.org/blink/trunk@153946 bbb929c8-8fbe-4397-9dbb-9b2b20218538