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The modern Xbox Elite Series 2 controller firmware reports on less axes
than the previous firmware. However, the only way to distinguish between
firmware versions is to check the length of the axes reported.

This change updates the mapping function to work for all firmware
versions by checking the axes length. On the older firmware, the axes
are shifted by one after axis 3 because axes 4 and 9 are redundancies.

BUG=1052543
TEST=Testing this requires two Xbox elite series 2 controllers, one with
     modern firmware and one with release firmware. When using them on
     production code users will notice that on pressing the DPAD on
     modern firmware either the triggers or the opposing dpad axis is
     pressed.

Change-Id: Ie51fd897a14180d664463d196b2fe744338c61c7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2057624Reviewed-by: Ovidio de Jesús Ruiz-Henríquez <odejesush@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>
Commit-Queue: José Torreguitar <jtguitar@google.com>
Cr-Commit-Position: refs/heads/master@{#742235}