[lacros] Encapsulates lacros test runner with test_env or xvfb

This CL encapsulates the lacros test runner with either xvfb.py or
test_env.py to be consistent with other Desktop platforms.

Bug: 1104318
Change-Id: I00980225aff8856e5747d15f7e57814fb2e4043c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2303169Reviewed-by: Dirk Pranke <dpranke@google.com>
Commit-Queue: Yuke Liao <liaoyuke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#789214}

testing/test.gni

@@ -374,14 +374,28 @@ template("test") {
     _executable = target_name
     _gen_runner_target = "${target_name}__runner"
 
+    if (defined(invoker.use_xvfb)) {
+      _use_xvfb = invoker.use_xvfb
+    } else {
+      _use_xvfb = false
+    }
+
     generate_wrapper(_gen_runner_target) {
       testonly = true
       wrapper_script = "$root_build_dir/bin/run_" + _executable
-      executable = "//build/lacros/test_runner.py"
+
+      if (_use_xvfb) {
+        executable = "//testing/xvfb.py"
+      } else {
+        executable = "//testing/test_env.py"
+      }
+
       executable_args = [
+        "@WrappedPath(../../build/lacros/test_runner.py)",
         "@WrappedPath(./${_executable})",
         "--test-launcher-bot-mode",
       ]
+
       if (is_asan) {
         executable_args += [ "--asan=true" ]
       }