[gin] Introduce Wrappable::GetObjectTemplate

gin/wrappable.cc

Index: gin/wrappable.cc
diff --git a/gin/wrappable.cc b/gin/wrappable.cc
index 4a9ef0e1935d32e0b7a5213ab6ec47a230d093db..68b84eca4875d57a513c3f50014f2cf30cbdbb29 100644
--- a/gin/wrappable.cc
+++ b/gin/wrappable.cc
@@ -17,9 +17,9 @@ WrappableBase::~WrappableBase() {
 }
 
 v8::Handle<v8::Object> WrappableBase::GetWrapperImpl(
-    v8::Isolate* isolate, WrapperInfo* wrapper_info) {
+    v8::Isolate* isolate, WrapperInfo* wrapper_info, TemplateBuilder builder) {
     if (wrapper_.IsEmpty())
-      CreateWrapper(isolate, wrapper_info);
+      CreateWrapper(isolate, wrapper_info, builder);
     return v8::Local<v8::Object>::New(isolate, wrapper_);
 }
 
@@ -31,10 +31,15 @@ void WrappableBase::WeakCallback(
 }
 
 v8::Handle<v8::Object> WrappableBase::CreateWrapper(v8::Isolate* isolate,
-                                                    WrapperInfo* info) {
+                                                    WrapperInfo* info,
+                                                    TemplateBuilder builder) {
   PerIsolateData* data = PerIsolateData::From(isolate);
   v8::Local<v8::ObjectTemplate> templ = data->GetObjectTemplate(info);
-  CHECK(!templ.IsEmpty());  // Don't forget to register an object template.
+  if (templ.IsEmpty()) {
+    templ = builder(isolate);
+    CHECK(!templ.IsEmpty());
+    data->SetObjectTemplate(info, templ);
+  }
   CHECK_EQ(kNumberOfInternalFields, templ->InternalFieldCount());
   v8::Handle<v8::Object> wrapper = templ->NewInstance();
   wrapper->SetAlignedPointerInInternalField(kWrapperInfoIndex, info);