Add getType/getPrivate to Value

Summary:
Adds:
 - getType so you can switch on type
 - getPrivate

Reviewed By: lexs

Differential Revision: D3515510

fbshipit-source-id: d574b04f563ac650bacec3751b50be6345e8439a

ReactCommon/cxxreact/Value.h

@@ -191,6 +191,11 @@ public:
     }
   }
 
+  template<typename ReturnType>
+  ReturnType* getPrivate() const {
+    return static_cast<ReturnType*>(JSObjectGetPrivate(m_obj));
+  }
+
   JSContextRef context() const {
     return m_context;
   }
@@ -223,6 +228,10 @@ public:
     return m_value;
   }
 
+  JSType getType() const {
+    return JSValueGetType(m_context, m_value);
+  }
+
   bool isBoolean() const {
     return JSValueIsBoolean(context(), m_value);
   }