[Android] Always precede Tap gesture events with TapDown
The gesture detector generates TapDown events before Tap events, but
there there remain cases where synthetic Tap events are not preceded
by such TapDown events. Insert the expected TapDown for these synthetic
cases, also validating this event ordering in the
GestureEventStreamValidator.
A consistent ordering here provides the render process, and any downstream
gesture listener, more context to reason about and react to the gesture
event stream.
BUG=418402
Review URL: https://codereview.chromium.org/724313003
Cr-Commit-Position: refs/heads/master@{#304611}
3 files changed
