Check for use_x11 before runnig desktop_capture_modules_tests on linux.

webrtc/modules/desktop_capture/BUILD.gn

Index: webrtc/modules/desktop_capture/BUILD.gn
diff --git a/webrtc/modules/desktop_capture/BUILD.gn b/webrtc/modules/desktop_capture/BUILD.gn
index bbf9ac57bbb6a7516f73ffae543cf468d54e59a0..441b0b392f9ef00171d896ff08dc97bd6162101a 100644
--- a/webrtc/modules/desktop_capture/BUILD.gn
+++ b/webrtc/modules/desktop_capture/BUILD.gn
@@ -37,8 +37,9 @@ if (rtc_include_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",