This change fixes two minor issues in Safari.
- In gr-diff-highlight, Safari does not support NodeList.forEach.
- In gr-diff-selection_test, a test that should have been failing (a
selection class was missing) was not being run in Chrome/CI. A prior
commit modified the CSS selectors that enable text selection, and the
test was not changed to reflect this.
SHA of the offending commit: 613b49c
Change-Id: I7ef3b017be9ae731496609430e3856f58e5bd24e