Add flutter_engine runtime to the test script so we can run standard dart tests from the test suite…

tools/testing/dart/test_suite.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.
 
 /**
  * Classes and methods for enumerating and preparing tests.
  *
  * This library includes:
  *
  * - Creating tests by listing all the Dart files in certain directories,
@@ skipping 190 matching lines @@
       String suffix = executableBinarySuffix;
       dartExecutable = useSdk
           ? '$buildDir/dart-sdk/bin/dart$suffix'
           : '$buildDir/dart$suffix';
     }
 
     TestUtils.ensureExists(dartExecutable, configuration);
     return dartExecutable;
   }
 
+  /// Returns the name of the Sky shell executable.

[Bill Hesse, 2017/01/05 17:48:33]

Should we use the name "flutter engine" everywhere, instead of both "flutter
engine" and "Sky shell"?

[siva, 2017/01/05 20:38:45]

Done.

+  String get skyBinaryFileName {
+    // Controlled by user with the option "--engine".
+    String skyExecutable = configuration['engine'];

[Bill Hesse, 2017/01/05 17:48:33]

If the default for this value in test_options was null, then you could just
write
configuration['engine'] ?? 'sky_shell'
Or the default should just be 'sky_shell' in the test_options option
declaration.

This code is in contradiction to the code in test_options which disallows this
case.

[siva, 2017/01/05 20:38:45]

Removed this default setting, the option is required for running flutter.

+
+    if (skyExecutable == '') {
+      skyExecutable = 'sky_shell';
+    }
+
+    TestUtils.ensureExists(skyExecutable, configuration);
+    return skyExecutable;
+  }
+
   String get dartVmNooptBinaryFileName {
     // Controlled by user with the option "--dart".
     String dartExecutable = configuration['dart'];
 
     if (dartExecutable == '') {
       String suffix = executableBinarySuffix;
       dartExecutable = useSdk
           ? '$buildDir/dart-sdk/bin/dart_noopt$suffix'
           : '$buildDir/dart_noopt$suffix';
     }
@@ skipping 2316 matching lines @@
       }
       if (path.length > WINDOWS_SHORTEN_PATH_LIMIT) {
         ++shortNameCounter;
         var pathEnd = path.substring(path.length - WINDOWS_PATH_END_LENGTH);
         path = "short${shortNameCounter}_$pathEnd";
       }
     }
     return path;
   }
 }