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This adds the feature and event definitions to the IPH backend for our
desktop IPH pilot feature: recommending users reopen accidentally
closed tabs. See associated issue for design doc, PRD, and mocks.

Bug: 887991
Change-Id: I939b0b8de95d7340d902ad2273c8bae0a751f12e
Reviewed-on: https://chromium-review.googlesource.com/c/1259476Reviewed-by: David Trainor <dtrainor@chromium.org>
Commit-Queue: Collin Baker <collinbaker@chromium.org>
Cr-Commit-Position: refs/heads/master@{#596366}