Create a separate section for HeapSnapshotWorker files in devtools.gypi

Also moved findBalancedCurlyBrackets from FileUtils.js to TextUtils.js

BUG=None
R=alph@chromium.org

Review URL: https://codereview.chromium.org/139633002

git-svn-id: svn://svn.chromium.org/blink/trunk@165388 bbb929c8-8fbe-4397-9dbb-9b2b20218538