Add support for function declarations and function expressions

pkg/kernel/testcases/interpreter/function_expressions_test.dart

+// Copyright (c) 2017, 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.
+
+library function_expression_test;
+
+main() {
+  var f = (int m, int n) => print('${m++}$n');
+  var a1 = 3;
+  var a2 = 7;
+
+  f(a1, a2);
+
+  int foo(int f1, String f2) {
+    print('$f1, $f2');
+    a1++;
+    return a1;
+  }
+
+  var m = foo(1, 'test');
+  print(m);
+  print(a1);
+
+  int bar(int i) {
+    if (i < 0 || i == 0) return 0;
+    return bar(--i);
+  }
+
+  print(bar(5));
+}