Use Xvfb in isolated testing only if use_x11 is set

ui/message_center/message_center_unittests.isolate

Index: ui/message_center/message_center_unittests.isolate
diff --git a/ui/message_center/message_center_unittests.isolate b/ui/message_center/message_center_unittests.isolate
index 7ad8cc3cf6d9b645cc367a17465e867d15ac5ef7..974cea942ff623704456294a8cfbebb32c3f6279 100644
--- a/ui/message_center/message_center_unittests.isolate
+++ b/ui/message_center/message_center_unittests.isolate
@@ -12,7 +12,7 @@
         ],
       },
     }],
-    ['OS=="linux"', {
+    ['OS=="linux" and use_x11==1', {
       'variables': {
         'command': [
           '../../testing/xvfb.py',
@@ -25,14 +25,14 @@
         ],
         'files': [
           '../../testing/xvfb.py',
-          '<(PRODUCT_DIR)/libosmesa.so',
+          '<(PRODUCT_DIR)/xdisplaycheck<(EXECUTABLE_SUFFIX)',
         ],
       },
     }],
-    ['OS=="linux" and use_ozone==0', {
+    ['OS=="linux"', {
       'variables': {
         'files': [
-          '<(PRODUCT_DIR)/xdisplaycheck<(EXECUTABLE_SUFFIX)',
+          '<(PRODUCT_DIR)/libosmesa.so',
         ],
       },
     }],
@@ -50,7 +50,7 @@
         ],
       },
     }],
-    ['OS=="mac" or OS=="win"', {
+    ['OS=="mac" or OS=="win" or use_ozone==1', {
       'variables': {
         'command': [
           '../../testing/test_env.py',