Move V8 snapshot loading code from isolate_holder to gin/v8_startup_data.{h,cc}.

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 b639d0640630e8821cb01ccd330b15e1eed8396f..723ab98dc405a5789de258681edfe424505d4230 100644
--- a/gin/test/file_runner.cc
+++ b/gin/test/file_runner.cc
@@ -17,12 +17,9 @@
 #include "gin/test/gc.h"
 #include "gin/test/gtest.h"
 #include "gin/try_catch.h"
+#include "gin/v8_initializer.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
-#ifdef V8_USE_EXTERNAL_STARTUP_DATA
-#include "gin/public/isolate_holder.h"
-#endif
-
 namespace gin {
 
 namespace {
@@ -63,11 +60,12 @@ void RunTestFromFile(const base::FilePath& path, FileRunnerDelegate* delegate,
   base::MessageLoop message_loop;
 
 #ifdef V8_USE_EXTERNAL_STARTUP_DATA
-  gin::IsolateHolder::LoadV8Snapshot();
+  gin::V8Initializer::LoadV8Snapshot();
 #endif
 
   gin::IsolateHolder::Initialize(gin::IsolateHolder::kStrictMode,
                                  gin::ArrayBufferAllocator::SharedInstance());
+
   gin::IsolateHolder instance;
   gin::ShellRunner runner(delegate, instance.isolate());
   {