Enabling 'gn check' on webrtc/sdk

BUG=webrtc:7499

Review-Url: https://codereview.webrtc.org/2818433003
Cr-Original-Commit-Position: refs/heads/master@{#17805}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 1e060c6b0cf72c805209820330968ea7d64208b7
7 files changed