GitLab

Runtimes should only be handled by the XRRuntimeManager. VRServiceImpl
needs to know if capabilities have changed, but does not need to know if
runtimes were added or removed, so we can merge those functions into one
and remove XRRuntime from VRServiceImpl, which will forward this end.
Also moved logic to check in the runtimes if an XRDeviceImpl is
presenting to the manager.

Bug: 842025
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: I4e155dbb4ff603572338a0d543ca030cd574ffb8
Reviewed-on: https://chromium-review.googlesource.com/1181685Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
Commit-Queue: Anna Offenwanger <offenwanger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584808}