Add readonly typings for Set and Map

Similar to ReadonlyArray, these typings remove the mutation methods from Set and Map so that they can only be initialized by the constructor.

Author: gmoothart

src/lib/es2015.collection.d.ts

@@ -15,6 +15,21 @@ interface MapConstructor {
 }
 declare var Map: MapConstructor;
 
+interface ReadonlyMap<K, V> {
+  forEach(
+      callbackfn: (value: V, index: K, map: ReadonlyMap<K, V>) => void,
+      thisArg?: any): void;
+  get(key: K): V|undefined;
+  has(key: K): boolean;
+  readonly size: number;
+}
+
+interface ReadonlyMapConstructor {
+  new<K, V>(entries?: [K, V][]): ReadonlyMap<K, V>;
+  readonly prototype: ReadonlyMap<any, any>;
+}
+declare var ReadonlyMap: ReadonlyMapConstructor;
+
 interface WeakMap<K, V> {
     delete(key: K): boolean;
     get(key: K): V | undefined;
@@ -45,6 +60,19 @@ interface SetConstructor {
 }
 declare var Set: SetConstructor;
 
+interface ReadonlySet<T> {
+  forEach(callbackfn: (value: T, index: T, set: ReadonlySet<T>) => void, thisArg?: any):
+      void;
+  has(value: T): boolean;
+  readonly size: number;
+}
+
+interface ReadonlySetConstructor {
+  new<T>(values?: T[]): ReadonlySet<T>;
+  readonly prototype: ReadonlySet<any>;
+}
+declare var ReadonlySet: ReadonlySetConstructor;
+
 interface WeakSet<T> {
     add(value: T): this;
     delete(value: T): boolean;