Add haptics to GamepadDataFetcher

A GamepadDataFetcher represents a host interface for receiving gamepad
state and communicating commands to a gamepad connected over a
particular host interface.

This CL modifies GamepadDataFetcher to support haptics commands.
Haptics commands received by GamepadService are routed to the fetcher
corresponding to the gamepad's host interface.

BUG=749295

Change-Id: I82629d34494871ed59c574a9846c0b4ff088f229
Reviewed-on: https://chromium-review.googlesource.com/739926
Commit-Queue: Matt Reynolds <mattreynolds@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#513009}
9 files changed