Enable exporting SSLKEYLOGFILE on Android w/ command line arguments

This moves handling of the SSLKEYLOGFILE environment variable from
//net to //chrome, and enables a command-line flag to support
Android builds. This has the side-effect of disabling the
SSLKEYLOGFILE support for //content-embedders, which must now
use SSLClientSocket::SetSSLKeyLogFile

Note that SSLClientSocket::SetSSLKeyLogFile is a temporary
solution until the SSLClientSocket can have its global context
broken up; in an ideal world, this would be a parameter off the
HttpNetworkSession::Params, and embedders should ideally handle
this environment variable similar to such params.

BUG=535184

Review URL: https://codereview.chromium.org/1403863002

Cr-Commit-Position: refs/heads/master@{#354562}
7 files changed