Use internalized strings for v8::Template::Set shorthand.

The string will be internalized anyhow when the first object is instantiated,
and since templates are eternal, the string will be eternal anyhow even if
the template is never instantiated.

Review-Url: https://codereview.chromium.org/2697683002
Cr-Commit-Position: refs/heads/master@{#43187}

include/v8.h

@@ -9077,7 +9077,7 @@ Local<Boolean> Boolean::New(Isolate* isolate, bool value) {
 }
 
 void Template::Set(Isolate* isolate, const char* name, Local<Data> value) {
-  Set(String::NewFromUtf8(isolate, name, NewStringType::kNormal)
+  Set(String::NewFromUtf8(isolate, name, NewStringType::kInternalized)
           .ToLocalChecked(),
       value);
 }