Fixing crash in video_render_tests in release mode.
Fixing crash in video_render_tests in release mode.

This is a test bug. Fixed usage of assert.

BUG=1917
R=mflodman@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/9979004

Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 6f9c48348b13021947909e594104c3c31fb270c9

sippet/webrtc,sippet/webrtc,sippet/webrtc,sippet/webrtc,sippet/webrtc,sippet/webrtc