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The palm suppression is enabled by an internal stylus enabled
TouchEventConverterEvdev via a callback to InputDeviceFactoryEvdev.
When in palm suppression mode, all internal touchscreen devices will
be disabled.
Before a touchscreen would lift all touches when disabled, and
re-initialize when re-enabled. To prevent the unnecessary ioctls the
code has been updated to force cancel all touches while disabled, but
continue to read and sync the internal touch state. This will also
make sure that touches that went down while disabled, will not
suddenly show up after enabling and continue to stay cancelled until
lifted.

BUG=636458

Review-Url: https://codereview.chromium.org/2263693003
Cr-Commit-Position: refs/heads/master@{#414860}