rtc::Buffer: Use RTC_DCHECK instead of assert

Review URL: https://codereview.webrtc.org/1749693002

Cr-Original-Commit-Position: refs/heads/master@{#11826}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: e3d99221c416ea2f5a1675667be26c14327afc75
2 files changed