Move Maybe template into v8.h so it can be used by SetResourceConstraints

src/globals.h

Index: src/globals.h
diff --git a/src/globals.h b/src/globals.h
index d0a57a4039f4d59ff0194f0cb4c537b635e7a9db..992f3a866f29d515927e8a3c80dc3cd64427b010 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -393,18 +393,6 @@ enum LanguageMode {
 };
 
 
-// A simple Maybe type, that can be passed by value.
-template<class T>
-struct Maybe {
-  Maybe() : has_value(false) {}
-  explicit Maybe(T t) : has_value(true), value(t) {}
-  Maybe(bool has, T t) : has_value(has), value(t) {}
-
-  bool has_value;
-  T value;
-};
-
-
 // The Strict Mode (ECMA-262 5th edition, 4.2.2).
 //
 // This flag is used in the backend to represent the language mode. So far