Set use_gtk=0 as default for Chromium builds.
Set use_gtk=0 as default for Chromium builds.

The files that are built when use_gtk==1 are not included in the Chromium build
(webrtc/media/devices/gtkvideorenderer.cc and webrtc/media/devices/gtkvideorenderer.h)
so to preserve previous behavior in Chromium before/after
https://codereview.webrtc.org/1587193006, this is the right thing to do.

The reason this was discovered was that a Chrome OS build started failing, since
it was lacking the gtk+2.0 package.

NOTRY=True
BUG=chromium:584722
TBR=tommi@webrtc.org

Review URL: https://codereview.webrtc.org/1677693002

Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#11510}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 1c24a6d5ca9613145c4a3a0f6b5f1f39232ba052

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