Win automatic toolchain: copy runtime dlls properly when not run from chrome/src.

gclient runhooks runs gyp_chromium from the chrome/ dir, but the script
was looking for out/ relative to that.

BUG=323300

Review URL: https://codereview.chromium.org/174063005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252500 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252500