Check for use_x11 before runnig desktop_capture_modules_tests on linux.

The tests need "x11/shared_x_display.h" which is not included when use_x11 is false and we're on linux.

The problem is:

screen_capturer_integration_test.cc
 - requires ->
screen_drawer.h
 - requires ->
screen_drawer_linux.cc
 - requires ->
x11/shared_x_display.h
 which is not included when use_x11 is false.

BUG=None
NOTRY=True

Review-Url: https://codereview.webrtc.org/2684683003
Cr-Commit-Position: refs/heads/master@{#16529}
diff --git a/webrtc/webrtc.gni b/webrtc/webrtc.gni
index 4c34eae..e6d746a 100644
--- a/webrtc/webrtc.gni
+++ b/webrtc/webrtc.gni
@@ -10,6 +10,7 @@
 import("//build/config/features.gni")
 import("//build/config/mips.gni")
 import("//build/config/sanitizers/sanitizers.gni")
+import("//build/config/ui.gni")
 import("//build_overrides/build.gni")
 import("//testing/test.gni")
 
@@ -172,7 +173,7 @@
 rtc_opus_dir = "//third_party/opus"
 
 # Desktop capturer is supported only on Windows, OSX and Linux.
-rtc_desktop_capture_supported = is_win || is_mac || is_linux
+rtc_desktop_capture_supported = is_win || is_mac || (is_linux && use_x11)
 
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