Add regression tests for two issues (7525, 7513).

tests/language/issue7513_test.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.
+
+// Regression test for issue 7513.
+
+foo(a, b) {
+  b[0] = 0.1;
+  return a * b[0];
+}
+
+main() {
+  var a = 0.1;
+  var b = [0.1];
+  for (var i = 0; i < 10000; i++) {
+    foo(a, b);
+  }
+  Expect.approxEquals(0.01, foo(a, b));
+}
+