Revert of mojo: make libmojo_public_test_support a static library.

mojo/public/c/test_support/BUILD.gn

Index: mojo/public/c/test_support/BUILD.gn
diff --git a/mojo/public/c/test_support/BUILD.gn b/mojo/public/c/test_support/BUILD.gn
index 75d9c13d346918ae5735ef7a850bd722f2d88cb0..592e80a63bd14c77ff5fb9afe504b13205397e79 100644
--- a/mojo/public/c/test_support/BUILD.gn
+++ b/mojo/public/c/test_support/BUILD.gn
@@ -2,15 +2,24 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-# GYP version: mojo/mojo_public.gyp:mojo_test_support
-static_library("test_support") {
+# GYP version: mojo/public/mojo_public.gyp:mojo_test_support
+shared_library("test_support") {
   output_name = "mojo_public_test_support"
+
+  defines = [ "MOJO_TEST_SUPPORT_IMPLEMENTATION" ]
 
   sources = [
     "test_support.h",
+    "test_support_export.h",
 
     # TODO(vtl): Convert this to thunks http://crbug.com/386799
     "../../tests/test_support_private.cc",
     "../../tests/test_support_private.h",
   ]
+
+  if (is_mac) {
+    # TODO(GYP)
+    #   # Make it a run-path dependent library.
+    #   'DYLIB_INSTALL_NAME_BASE': '@loader_path',
+  }
 }