Switch to downloaded SDK executable, drop executables in testing/bin.

tools/testing/dart/test_runner.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 executing tests.
  *
  * This module includes:
  * - Managing parallel execution of tests, including timeout checks.
  * - Evaluating the output of each test as pass/fail/crash/timeout.
@@ skipping 274 matching lines @@
   }
 
   bool _equal(BrowserTestCommand other) =>
       super._equal(other) &&
       browser == other.browser &&
       url == other.url &&
       identical(configuration, other.configuration) &&
       retry == other.retry;
 
   String get reproductionCommand {
-    var parts = [TestUtils.dartTestExecutable.toString(),
+    var parts = [Platform.resolvedExecutable,
                 'tools/testing/dart/launch_browser.dart',
                 browser,
                 url];
     return parts.map(escapeCommandLineArgument).join(' ');
   }
 
   int get maxNumRetries => 4;
 }
 
 class BrowserHtmlTestCommand extends BrowserTestCommand {
@@ skipping 2660 matching lines @@
     }
   }
 
   void eventAllTestsDone() {
     for (var listener in _eventListener) {
       listener.allDone();
     }
     _allDone();
   }
 }