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With this CL we initate the module install once the user enters VR on a
WebXR/VR page. In more detail this CL

- Introduces native VrModuleDelegate used to request VR module from
  native,

- Refactors GvrDevice to request the VR module as part of its
  initialization flow,

- Adds native side of the VrModuleProvider for Java-native
  communication.

Bug: 862689
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: I960d2bdd4d2c64a19fa6069e457d44f77ab0e73b
Reviewed-on: https://chromium-review.googlesource.com/c/1241458
Commit-Queue: Tibor Goldschwendt <tiborg@chromium.org>
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Reviewed-by: Bill Orr <billorr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#602922}