Add tools/perf/internal to .gitignore .

This needs to land in preparation for mapping internal perf tests
from src-internal onto the main tree.

R=tonyg@chromium.org, nduca@chromium.org, dtu@chromium.org
BUG=345853

Review URL: https://codereview.chromium.org/225103003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@261676 0039d316-1c4b-4281-b951-d872f2087c98

.gitignore

@@ -357,6 +357,7 @@ v8.log
 /tools/metrics/histograms/histograms.before.pretty-print.xml
 /tools/page_cycler/acid3
 /tools/perf/data
+/tools/perf/internal
 /tools/perf/results.html
 /tools/swarming_client
 /tools/tryserver