Stoppp using trippple consonants

tests/language/library_env_test.dart

 // Copyright (c) 2015, 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';
 
 main() {
   const NOT_PRESENT = false;
 
   Expect.isTrue(const bool.fromEnvironment("dart.library.async"));
@@ skipping 41 matching lines @@
         const bool.fromEnvironment("dart.library.web_sql",
             defaultValue: NOT_PRESENT));
   }
 
   bool hasIoSupport;
   hasIoSupport = true; //  //# has_io_support: ok
   hasIoSupport = false; // //# has_no_io_support: ok
 
   if (hasIoSupport != null) {
     // Dartium overrides 'dart.library.io' to return "false".
-    // We don't test for the non-existance, but just make sure that
+    // We don't test for the non-existence, but just make sure that
     // dart.library.io is not set to true.
     Expect.equals(hasIoSupport,
         const bool.fromEnvironment("dart.library.io", defaultValue: false));
   }
 
   bool hasMirrorSupport;
   hasMirrorSupport = true; //  //# has_mirror_support: ok
   hasMirrorSupport = false; // //# has_no_mirror_support: ok
 
   if (hasMirrorSupport != null) {
@@ skipping 17 matching lines @@
       NOT_PRESENT,
       const bool.fromEnvironment("dart.library.converT",
           defaultValue: NOT_PRESENT));
   Expect.equals(NOT_PRESENT,
       const bool.fromEnvironment("dart.library.", defaultValue: NOT_PRESENT));
   Expect.equals(
       NOT_PRESENT,
       const bool.fromEnvironment("dart.library.core ",
           defaultValue: NOT_PRESENT));
 }