Add LogDog stream name normalization function.

Add a LogDog stream normalization function. This will take an arbitrary
stream name and make a best-effort attempt to convert it to a valid
LogDog stream name.

BUG=chromium:628770
TEST=unittest
  - Unit test for the new function runs successfully.

Review-Url: https://codereview.chromium.org/2243483003
NOKEYCHECK=True
GitOrigin-RevId: 6a5120210cd8214bcbaec031333e3148520d57df