Implement support for specifying string interopolation style variable substitution in the import ...

tests/vm/src/test1.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.
+//
+// VMOptions=--import_map=GOOGLE,. --import_map=SRC,mysrc --import_map=DART,.
+//
+// Dart test program for checking implementation of string
+// interapolation feature in import statements.
+
+#library('test1.dart');
+
+#import('${GOOGLE}/$SRC/test2.dart');
+#import('$SRC/test3.dart');
+
+int test1() {
+  return 1;
+}
+
+main() {
+  var result = test1() + test2() + test3();
+  Expect.equals(6, result);
+}