Test annotations were added to all tests but PeerConnectionClientTest.testLoopbackVp9 in https://codereview.webrtc.org/1876233002. Recent changes in the Chromium toolchain now makes the test fail if annotations are missing. TBR=phoglund@webrtc.org Review URL: https://codereview.webrtc.org/1962533002 . Cr-Commit-Position: refs/heads/master@{#12658}