Fix bad generate-at-use-site.

tests/language/pure_function_test.dart

+// Copyright (c) 2014, 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.
+
+import "package:expect/expect.dart";
+
+// Regression test for issue 17483.
+
+class A {
+  var x, y;
+  A(x, this.y) {
+    this.x = x;
+  }
+  toString() => "a";
+}
+
+foo(trace) => trace.add("foo");
+bar(trace) => trace.add("bar");
+
+main() {
+  var trace = [];
+  // Dart2js must keep the order of t1 and t2.
+  var t1 = foo(trace);
+  var t2 = bar(trace);
+  // Dart2js inlines the constructor, yielding something like:
+  //   t3 = jsNew A(null, t2);  // Note that jsNew is pure.
+  //   t3.x = t1;
+  // t3 is used twice and cannot be generated at use site.
+  // Dart2js must not allow t1 to cross the t3-line.
+  var a = new A(t1, t2);
+  // Use a. It is already implicitly used by the this.x = x line in its
+  // constructor. With the following use we use it twice and make sure that
+  // the allocation can not be generated at use-site.
+  trace.add(a.toString());
+  Expect.listEquals(["foo", "bar", "a"], trace);
+}