Refactor IsolateHolder to be able to always create the isolate

gin/test/file_runner.cc

Index: gin/test/file_runner.cc
diff --git a/gin/test/file_runner.cc b/gin/test/file_runner.cc
index a3872890dc9ec497ba85697332d36131e2e6effd..83228d6d014e5570a63847f149dca2df58941b07 100644
--- a/gin/test/file_runner.cc
+++ b/gin/test/file_runner.cc
@@ -7,6 +7,7 @@
 #include "base/files/file_util.h"
 #include "base/message_loop/message_loop.h"
 #include "base/path_service.h"
+#include "gin/array_buffer.h"
 #include "gin/converter.h"
 #include "gin/modules/console.h"
 #include "gin/modules/module_registry.h"
@@ -57,7 +58,9 @@ void RunTestFromFile(const base::FilePath& path, FileRunnerDelegate* delegate,
 
   base::MessageLoop message_loop;
 
-  gin::IsolateHolder instance(gin::IsolateHolder::kStrictMode);
+  gin::IsolateHolder::Initialize(gin::IsolateHolder::kStrictMode,
+                                 gin::ArrayBufferAllocator::SharedInstance());
+  gin::IsolateHolder instance;
   gin::ShellRunner runner(delegate, instance.isolate());
   {
     gin::Runner::Scope scope(&runner);