gclient_scm: Assume URLs containing 'googlesource' are for Git repos
gclient_scm: Assume URLs containing 'googlesource' are for Git repos

Fixes this flow, which currently assumes we're using an svn checkout:

gclient config https://chromium.googlesource.com/chromium/blink
gclient sync

BUG=

Review URL: https://codereview.chromium.org/246903005

git-svn-id: bd64dd6fa6f3f0ed0c0666d1018379882b742947@265369 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

svn2github/chromium-depot-tools,svn2github/chromium-depot-tools,svn2github/chromium-depot-tools