Touch input support for Windows

Had to add some logic to avoid touch and mouse cross-talk, because
(at least on my laptop), the touch screen generates both kinds of
events.

This seems really useful [1] for the many [2] Skia developers with
touch-enabled Windows devices.

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1: No, not really.
2: N = 1?

Bug: skia:
Change-Id: Ib888bf4198f2cc0a29a31581ec4b64d3d9008c33
Reviewed-on: https://skia-review.googlesource.com/18920
Reviewed-by: Yuqian Li <liyuqian@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
5 files changed