Add a new metric for gesture typing events, with an accompanying new enum.
Add a new metric for gesture typing events, with an accompanying new enum.

BUG=None
Test=None

Review URL: https://codereview.chromium.org/1308423002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#345194}

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