Make gles2::MemoryTracker non-refcounted

It's not needed and removing refcounting makes it a pure interface.

Bug: None
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: I4437dd932200daf4637175b40cf894089dc020be
Reviewed-on: https://chromium-review.googlesource.com/1142735
Reviewed-by: Jonathan Backer <backer@chromium.org>
Commit-Queue: Antoine Labour <piman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576646}
14 files changed