Check for use_x11 before runnig desktop_capture_modules_tests on linux.

webrtc/modules/desktop_capture/BUILD.gn

 # Copyright (c) 2014 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 import("//build/config/ui.gni")
 import("../../webrtc.gni")
@@ skipping 19 matching lines @@
     "../..:webrtc_common",
     "../../base:rtc_base",  # TODO(kjellander): Cleanup in bugs.webrtc.org/3806.
   ]
 }
 
 if (rtc_include_tests) {
   rtc_source_set("desktop_capture_modules_tests") {
     testonly = true
     sources = []
     deps = []
-    if (rtc_desktop_capture_supported) {
+    if ((!is_linux || use_x11) && rtc_desktop_capture_supported) {

[kjellander_webrtc, 2017/02/09 13:59:50]

This is somewhat hard to read.
What about to change
https://cs.chromium.org/chromium/src/third_party/webrtc/webrtc.gni?rcl=a48313...
like:
rtc_desktop_capture_supported = is_win || is_mac || (is_linux && use_x11)
if the problem is that these tests are failing when X11 is not enabled?

[Sergey Ulanov, 2017/02/09 18:52:22]

There is an issue with Chrome OS and Android. There are no screen capturers for
ChromeOS or Android in WebRTC repo, but screen capturing is still supported in
chrome, it's just implemented in chromium instead of in webrtc. These screen
capturers may still depend on on some classes currently in desktop_capturer
module (e.g. DesktopRegion), so we don't want to disable all unittests
completely. Currently rtc_desktop_capture_supported disables all tests, see
desktop_capture_unittests. 

I think we should use rtc_desktop_capture_supported to indicate that screen
capturer is implemented in WebRTC. Then it makes sense setting it to "is_win ||
is_mac || (is_linux && use_x11)", but desktop_capture_unittests should be
updated to handle it properly. Right now it's already hacked for android - see
is_android condition there.
I suggest updating desktop_capture_unittests target to always include all deps
and all tests except screen_capturer*unittest.cc. The screen_capturer* tests
should be enabled only when rtc_desktop_capture_supported=true.

       deps += [
+        ":desktop_capture",
         ":desktop_capture_mock",
         ":primitives",
         ":screen_drawer",
         "../../base:rtc_base",
         "../../base:rtc_base_approved",
         "../../system_wrappers:system_wrappers",
         "../../test:test_support",
         "../../test:video_test_support",
       ]
       sources += [
@@ skipping 249 matching lines @@
     sources = [
       "differ_vector_sse2.cc",
       "differ_vector_sse2.h",
     ]
 
     if (is_posix) {
       cflags = [ "-msse2" ]
     }
   }
 }