Inline String isEmpty, refactor inlining of intrinsics.

tests/language/string_intrinsics_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.
+// Replace with shared test once interface issues clarified.
+// Test various String intrinsics
+
+main() {
+  var oneByte = "Hello world";
+  var empty = "";
+  for (int i = 0; i < 6000; i++) {
+    Expect.equals(11, testLength(oneByte));
+    Expect.equals(0, testLength(empty));
+    Expect.isFalse(testIsEmpty(oneByte));
+    Expect.isTrue(testIsEmpty(empty));
+  }
+}
+
+
+testLength(s) {
+  return s.length;
+}
+
+
+testIsEmpty(s) {
+  return s.isEmpty();
+}