EDK: Split the mojo_edk_system_unittests target.

mojo/edk/BUILD.gn

Index: mojo/edk/BUILD.gn
diff --git a/mojo/edk/BUILD.gn b/mojo/edk/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..c9f2046aea70a9b98f121dc59ff4416c58532889
--- /dev/null
+++ b/mojo/edk/BUILD.gn
@@ -0,0 +1,14 @@
+# Copyright 2015 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+group("tests") {
+  testonly = true
+  deps = [
+    "embedder:mojo_edk_embedder_unittests",
+    "system:mojo_edk_system_perftests",
+    "system:mojo_edk_system_unittests",
+    "system/test:mojo_edk_system_test_unittests",
+    "util:mojo_edk_util_unittests",
+  ]
+}