GitLab

Adds a few simple signals for a Tap gesture relative to the content
that was tapped.  These signals include word length and tap offset.
Logs UMA for CTR when these signals are present.

Updates the CS Context with analysis of the content where the Tap
gesture occurred.

One signal determines if the user tapped near the edge of a word
or not. The rest look at very short words, or relatively long words.

All signals use the existing CSHeuristics framework to do the checking and logging.

Updates the CSHeuristics framework to make the CSContext available
to heuristics so they can inspect the text tapped before deciding
whether to suppress or not.

Adds Field Trial params to enable actual suppression based on
these new signals (likely to be used only for interactive-testing
and demonstration purposes).

BUG=723194

Review-Url: https://codereview.chromium.org/2906763002
Cr-Commit-Position: refs/heads/master@{#476485}