[Draft] try out the idea of adding export macros for C++ bindings.

mojo/public/cpp/bindings/tests/BUILD.gn

Index: mojo/public/cpp/bindings/tests/BUILD.gn
diff --git a/mojo/public/cpp/bindings/tests/BUILD.gn b/mojo/public/cpp/bindings/tests/BUILD.gn
index 33610fd3858553c49e32a8c64512fda89bc2bc52..34d11e041a85612600173ddb01c5debbadd059f6 100644
--- a/mojo/public/cpp/bindings/tests/BUILD.gn
+++ b/mojo/public/cpp/bindings/tests/BUILD.gn
@@ -94,3 +94,22 @@ source_set("mojo_public_bindings_test_utils") {
     "//mojo/public/c/system",
   ]
 }
+
+component("tests_component") {
+  testonly = true
+  defines = [ "CONTENT_IMPLEMENTATION" ]
+  deps = [
+     ":tests",
+    "//third_party/mojo/src/mojo/edk/system",
+#    "//mojo/public/interfaces/bindings/tests:test_interfaces",
+#    ":mojo_public_bindings_test_utils",
+#    "//mojo/common",
+#    "//mojo/environment:chromium",
+#    "//mojo/message_pump",
+#    "//mojo/public/cpp/bindings",
+#    "//mojo/public/cpp/bindings:callback",
+#    "//mojo/public/cpp/system",
+#    "//mojo/public/cpp/test_support:test_utils",
+#    "//mojo/public/cpp/utility",
+  ]
+}