GN build rules for all unit test targets in mojo/

mojo/shell/BUILD.gn

Index: mojo/shell/BUILD.gn
diff --git a/mojo/shell/BUILD.gn b/mojo/shell/BUILD.gn
index c5482df60b3e294ce51b5064dcde0e69aded6e6b..cb3ec5abb0cd92cf30b8da2cc9d44961a3dda64d 100644
--- a/mojo/shell/BUILD.gn
+++ b/mojo/shell/BUILD.gn
@@ -164,3 +164,20 @@ test("mojo_shell_tests") {
     ]
   }
 }
+
+# GYP version: mojo/mojo.gyp:mojo_shell_test_support
+source_set("test_support") {
+  sources = [
+    "shell_test_helper.cc",
+    "shell_test_helper.h",
+  ]
+
+  deps = [
+    ":lib",
+    "//base",
+    "//base:base_static",
+    "//mojo/application_manager",
+    "//mojo/system",
+    "//url",
+  ]
+}