Introduce a Gin class instead of using global functions to control gin

mojo/public/bindings/js/test/run_all_unittests.cc

Index: mojo/public/bindings/js/test/run_all_unittests.cc
diff --git a/mojo/public/bindings/js/test/run_all_unittests.cc b/mojo/public/bindings/js/test/run_all_unittests.cc
index a6e4ef6154a1230710243b7dcf6fcb28632eb406..ee7f89c47381ebd1a74a5bcce00d13367242f952 100644
--- a/mojo/public/bindings/js/test/run_all_unittests.cc
+++ b/mojo/public/bindings/js/test/run_all_unittests.cc
@@ -7,13 +7,11 @@
 #include "base/compiler_specific.h"
 #include "base/test/launcher/unit_test_launcher.h"
 #include "base/test/test_suite.h"
-#include "gin/initialize.h"
 #include "mojo/system/core_impl.h"
 
 int main(int argc, char** argv) {
   base::TestSuite test_suite(argc, argv);
 
-  gin::Initialize();
   mojo::system::CoreImpl::Init();
 
   return base::LaunchUnitTests(