[mjsunit] Change assertThrows such that it can check the exception message.

test/mjsunit/regress/regress-2263.js

Index: test/mjsunit/regress/regress-2263.js
diff --git a/test/mjsunit/regress/regress-2263.js b/test/mjsunit/regress/regress-2263.js
index 9a9db58773b18af75e686f8d11b607de867fde53..9e4b079bdc61af52a3c9e630e19a20ff6bde0ceb 100644
--- a/test/mjsunit/regress/regress-2263.js
+++ b/test/mjsunit/regress/regress-2263.js
@@ -25,6 +25,30 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+assertThrows = function assertThrows(code, type_opt, cause_opt) {
+  var threwException = true;
+  try {
+    if (typeof code === 'function') {
+      code();
+    } else {
+      eval(code);
+    }
+    threwException = false;
+  } catch (e) {
+    if (typeof type_opt === 'function') {
+      assertInstanceof(e, type_opt);
+    } else if (type_opt !== void 0) {
+      failWithMessage("invalid use of assertThrows, maybe you want assertThrowsEquals");
+    }
+    if (arguments.length >= 3) {
+      assertEquals(e.type, cause_opt);
+    }
+    // Success.
+    return;
+  }
+  failWithMessage("Did not throw exception");
+};
+
 var obj = { length: { valueOf: function(){ throw { type: "length" }}}};
 var sep = { toString: function(){ throw { type: "toString" }}};
 assertThrows("Array.prototype.join.call(obj, sep)", undefined, "length");