Make gclient warn when svn is used.
Make gclient warn when svn is used.

Include links to the tracking bug and to request creating git repositories. Also
include note how to keep subversion support, if users require this.

It won't warn when git-svn clones are used.

There is no functional change except printing a warning to stderr.

Remove stale code. The CHROMIUM_SRC_URL variable is also defined in gclient.py
so it looks like a copy-paste error.

R=iannucci@chromium.org
BUG=475320

Review URL: https://codereview.chromium.org/1154173003

git-svn-id: fd409f4bdeea2bb50a5d34bb4d4bfc2046a5a3dd@295478 0039d316-1c4b-4281-b951-d872f2087c98

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