Added a stringContaining asymmetric equality tester

* Fixes #1923.

src/core/base.js

@@ -319,6 +319,17 @@ getJasmineRequireObj().base = function(j$, jasmineGlobal) {
     return new j$.StringMatching(expected);
   };
 
+  /**
+   * Get a matcher, usable in any {@link matchers|matcher} that uses Jasmine's equality (e.g. {@link matchers#toEqual|toEqual}, {@link matchers#toContain|toContain}, or {@link matchers#toHaveBeenCalledWith|toHaveBeenCalledWith}),
+   * that will succeed if the actual value is a `String` that contains the specified `String`.
+   * @name jasmine.stringContaining
+   * @function
+   * @param {String} expected
+   */
+  j$.stringContaining = function(expected) {
+    return new j$.StringContaining(expected);
+  };
+
   /**
    * Get a matcher, usable in any {@link matchers|matcher} that uses Jasmine's equality (e.g. {@link matchers#toEqual|toEqual}, {@link matchers#toContain|toContain}, or {@link matchers#toHaveBeenCalledWith|toHaveBeenCalledWith}),
    * that will succeed if the actual value is an `Array` that contains at least the elements in the sample.