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

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index ba4d19b01d45bba7981f4849eafcd81acc49ad37..73bf3281a38a1040bbdcb791895eb378b11d6820 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -877,6 +877,21 @@ class V8_EXPORT HandleScope {
 };
 
 
+/**
+ * A simple Maybe type, representing an object which may or may not have a
+ * 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;
+};
+
+
 // --- Special objects ---