Reland "Don't refcount tracking id -> slot id mapping."
Previously we tried to refcount the tracking id to slot id mapping.
This broke in some circumstances where the number of press events was
not equal to the number of release events.
This patch switches to marking some touch events such that they don't
modify the mapping, simplifying logic, and fixing a nasty bug.
Initially landed here:
https://codereview.chromium.org/
785753002/
Reverted here:
https://codereview.chromium.org/
869433007/
due to memory failures.
BUG=439051
TEST=EventsXTest.TouchEventNotRemovingFromNativeMapping
Review URL: https://codereview.chromium.org/
886593004
Cr-Commit-Position: refs/heads/master@{#314327}