The ANGLE platform methods layer is imported on multiple
OS configs. This rule change should allow better parsing
of the platform header dependencies by the bot analyze
step.

BUG=778918

Cq-Include-Trybots: 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
Change-Id: I2fd1e4b9b7cf2b89c3e7dce406b28afd7ad21d06
Reviewed-on: https://chromium-review.googlesource.com/767490


Reviewed-by: Antoine Labour <piman@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Cr-Commit-Position: refs/heads/master@{#516123}