Pinch zoom detection is updated

Pinch zoom event is detected if the two fingers have been moving
in opposite directions for all the history that we have in
state_buffer_. Thumb detection also is modified to allow pinch
zoom with thumb.
This patch will cause a delay in move gesture detection if gesturing
finger arrives with thumb. This delay only happens if pinch zoom is
enabled.

BUG=none
TEST=none

Change-Id: I22fd08705656286976f2fb31de04b26c9d2ef72e
Reviewed-on: https://chromium-review.googlesource.com/312234
Commit-Ready: Amirhossein Simjour <asimjour@chromium.org>
Tested-by: Amirhossein Simjour <asimjour@chromium.org>
Reviewed-by: Andrew de los Reyes <adlr@chromium.org>
3 files changed