Build SharedExclusiveLock in Chromium.
Build SharedExclusiveLock in Chromium.

Partially un-breaks the Chromium FYI build.

TBR=jbauch@webrtc.org, tommi@webrtc.org
BUG=

Review URL: https://codereview.webrtc.org/1739713002 .

Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#11765}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: a5d8e4eef58574ddb4c4c818de71491a52887f45

Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,jchavanton/webrtc,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,jchavanton/webrtc,jchavanton/webrtc,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,jchavanton/webrtc,jchavanton/webrtc,jchavanton/webrtc,jchavanton/webrtc,Alkalyne/webrtctrunk