Reduce run-time of two longest running tests (checked mode).

tests/language/src/MathVMTest.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 // Tests that the VM does not crash on weird corner cases of class Math.
+// VMOptions=--optimization_invocation_threshold=100
 
 class FakeNumber {
   const FakeNumber();
   void toDouble() {}
 }
 
 class MathTest {
   static bool testParseInt(x) {
     try {
       Math.parseInt(x);  // Expects string.
@@ skipping 11 matching lines @@
       return false;
     }
   }
 
   static void testMain() {
     Expect.equals(false, testParseInt(5));
     Expect.equals(false, testSqrt(const FakeNumber()));
   }
 }
 main() {
-  for (int i = 0; i < 2000; i++) {
+  for (int i = 0; i < 200; i++) {
     MathTest.testMain();
   }
 }