refactor: migrate dialog API to //gin (#19482)

* get ShowMessageBoxSync working with gin

* move more dialog methods

* all methods moved

* cleanup

* add util func for template creation

shell/common/api/gin_utils.h

@@ -0,0 +1,27 @@
+// Copyright (c) 2019 GitHub, Inc.
+// Use of this source code is governed by the MIT license that can be
+// found in the LICENSE file.
+
+#ifndef SHELL_COMMON_API_GIN_UTILS_H_
+#define SHELL_COMMON_API_GIN_UTILS_H_
+
+#include "gin/function_template.h"
+
+namespace gin {
+
+// NOTE: V8 caches FunctionTemplates. Therefore it is user's responsibility
+// to ensure this function is called for one type only ONCE in the program's
+// whole lifetime, otherwise we would have memory leak.
+template <typename Sig>
+v8::Local<v8::Function> ConvertCallbackToV8Leaked(
+    v8::Isolate* isolate,
+    const base::RepeatingCallback<Sig>& callback) {
+  // LOG(WARNING) << "Leaky conversion from callback to V8 triggered.";
+  return gin::CreateFunctionTemplate(isolate, callback)
+      ->GetFunction(isolate->GetCurrentContext())
+      .ToLocalChecked();
+}
+
+}  // namespace gin
+
+#endif  // SHELL_COMMON_API_GIN_UTILS_H_