[chromecast] Fix back gesture behavior.

Changes the back gesture behavior to match UX expectations.

  - Do not trigger the back gesture until the finger lifts.
  - Make sure progress events never continue after cancel or end.

Bug: internal b/109888887
Test: manual and unit tests
Change-Id: I388e078d4ec520e53bfed34dfdaaa378dadf0d0a
Reviewed-on: https://chromium-review.googlesource.com/1135188
Commit-Queue: Ryan Daum <rdaum@chromium.org>
Reviewed-by: Alex Sakhartchouk <alexst@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574563}
2 files changed