VR: Use PlatformController interface for the GestureDetector

This is a step towards making the GestureDetector detect gestures
triggered by other buttons of the PlatformController.

Bug: 865486
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:linux_vr;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: Ifbdfc28b850fae81446e21caf42027506f7bf522
Reviewed-on: https://chromium-review.googlesource.com/1143712
Commit-Queue: Aldo Culquicondor <acondor@chromium.org>
Reviewed-by: Amirhossein Simjour <asimjour@chromium.org>
Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576948}
7 files changed