Add support to dart2js for option --enable-asserts.

tools/testing/dart/options.dart

 // Copyright (c) 2013, 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 'dart:io';
 
 import 'configuration.dart';
 import 'drt_updater.dart';
 import 'path.dart';
 import 'utils.dart';
@@ skipping 159 matching lines @@
     new _Option('system', 'The operating system to run tests on.',
         abbr: 's', values: System.names, defaultsTo: Platform.operatingSystem),
     new _Option.bool('checked', 'Run tests in checked mode.'),
     new _Option.bool('strong', 'Run tests in strong mode.'),
     new _Option.bool('host_checked', 'Run compiler in checked mode.'),
     new _Option.bool('minified', 'Enable minification in the compiler.'),
     new _Option.bool(
         'csp', 'Run tests under Content Security Policy restrictions.'),
     new _Option.bool(
         'fast_startup', 'Pass the --fast-startup flag to dart2js.'),
+    new _Option.bool('enable_asserts',
+        'Pass the --enable-asserts flag to dart2js or to the vm.'),
     new _Option.bool('dart2js_with_kernel',
         'Enable the internal pipeline in dart2js to use kernel.'),
     new _Option.bool('hot_reload', 'Run hot reload stress tests.'),
     new _Option.bool(
         'hot_reload_rollback', 'Run hot reload rollback stress tests.'),
     new _Option.bool('use_blobs',
         'Use mmap instead of shared libraries for precompilation.'),
     new _Option.int('timeout', 'Timeout in seconds.', abbr: 't'),
     new _Option(
         'progress',
@@ skipping 406 matching lines @@
                 isVerbose: data["verbose"] as bool,
                 listTests: data["list"] as bool,
                 printTiming: data["time"] as bool,
                 printReport: data["report"] as bool,
                 reportInJson: data["report_in_json"] as bool,
                 resetBrowser: data["reset_browser_configuration"] as bool,
                 skipCompilation: data["skip_compilation"] as bool,
                 useBlobs: data["use_blobs"] as bool,
                 useSdk: data["use_sdk"] as bool,
                 useFastStartup: data["fast_startup"] as bool,
+                useEnableAsserts: data["enable_asserts"] as bool,
                 useDart2JSWithKernel: data["dart2js_with_kernel"] as bool,
                 writeDebugLog: data["write_debug_log"] as bool,
                 writeTestOutcomeLog: data["write_test_outcome_log"] as bool,
                 drtPath: data["drt"] as String,
                 dartiumPath: data["dartium"] as String,
                 chromePath: data["chrome"] as String,
                 safariPath: data["safari"] as String,
                 firefoxPath: data["firefox"] as String,
                 dartPath: data["dart"] as String,
                 dartPrecompiledPath: data["dart_precompiled"] as String,
@@ skipping 147 matching lines @@
       if (name == option.name) return option;
 
       // Allow hyphens instead of underscores as the separator since they are
       // more common for command line flags.
       if (name == option.name.replaceAll("_", "-")) return option;
     }
 
     return null;
   }
 }