[dart_fuchsia_test] pass through test environments.

Needed so that callers of dart_fuchsia_test can specify environments.
See bug for context.

Bug: IN-927 #comment
Test: CQ
Change-Id: Ia54f22073c923b124eeccb8463e5710ce3dead87
diff --git a/dart/dart_fuchsia_test.gni b/dart/dart_fuchsia_test.gni
index 72fc225..4cca90f 100644
--- a/dart/dart_fuchsia_test.gni
+++ b/dart/dart_fuchsia_test.gni
@@ -30,6 +30,10 @@
 #     being run automatically.
 #     Defaults to False.
 #
+#   environments (optional)
+#      Device environments this test should run in. Passed through to
+#      package.tests.environments in //build/package.gni.
+#
 # Example of usage:
 #
 #   dart_fuchsia_test("some_tests") {
@@ -104,6 +108,9 @@
         {
           name = generated_run_test_sh_target
           dest = target_name
+          if (defined(invoker.environments)) {
+            environments = invoker.environments
+          }
         },
       ]
     }