And get rid of the few already unused includes of non_thread_safe.h

BUG=676387
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

TBR=gab@chromium.org (for unused includes)
TBR=thestig@chromium.org (for removing unused NonThreadSafe)

Review-Url: https://codereview.chromium.org/2921903003
Cr-Commit-Position: refs/heads/master@{#477305}