Disable video capture service by default on Linux.

Suspect of making WebRTC Linux Tester bot fail almost reliably.

First failure:
https://build.chromium.org/deprecated/chromium.webrtc/builders/Linux%20Tester/builds/33590

Most recent failure:
https://build.chromium.org/deprecated/chromium.webrtc/builders/Linux%20Tester/builds/33669

Will revert if this does not fix the bot.

TBR=chfremer@chromium.org

Bug: 721812
Change-Id: Ic819219a5b39ad66cce9a1cb9a426a3f2836c541
Reviewed-on: https://chromium-review.googlesource.com/817995Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Commit-Queue: Guido Urdaneta <guidou@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523080}

services/video_capture/public/cpp/constants.cc

@@ -10,8 +10,7 @@ namespace video_capture {
 
 const base::Feature kMojoVideoCapture {
   "MojoVideoCapture",
-#if (defined(OS_LINUX) && !defined(OS_CHROMEOS)) || defined(OS_MACOSX) || \
-    defined(OS_WIN)
+#if defined(OS_MACOSX) || defined(OS_WIN)
       base::FEATURE_ENABLED_BY_DEFAULT
 #else
       base::FEATURE_DISABLED_BY_DEFAULT