[ET] Update *New* text styling in the context menu.

This makes the "New" text be a superscript, smaller, and colored.

This also makes some minor updates to the SpanApplier:
1) Ability to apply multiple spans to the same region.
2) Changes the doc to say that applying a null span does nothing.


Change-Id: Ifb49fa091d7a2f8a0e07e5ab8b12299eba33d585
Reviewed-on: https://chromium-review.googlesource.com/c/1393674
Commit-Queue: Donn Denman <donnd@chromium.org>
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Reviewed-by: Theresa <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622265}
7 files changed