Add dart2snapshot compiler and dart_snapshotted runtime to test scripts

tools/testing/dart/test_options.dart

Index: tools/testing/dart/test_options.dart
diff --git a/tools/testing/dart/test_options.dart b/tools/testing/dart/test_options.dart
index 8e23169fea7e59c3f641d50db9ec1ab32b75252a..990de7aec4fb9432b537b99ca1508cd4b5c9db03 100644
--- a/tools/testing/dart/test_options.dart
+++ b/tools/testing/dart/test_options.dart
@@ -65,9 +65,13 @@ class TestOptionsParser {
          none (compile only)),
 
    dart2analyzer: Perform static analysis on Dart code by running the analyzer
-          (only valid with the following runtimes: none)''',
+          (only valid with the following runtimes: none)
+
+   dart2snapshot: Compile the Dart code into a snapshot before running the test
+          (only valid with the following runtimes: dart_snapshotted)''',
               ['-c', '--compiler'],
-              ['none', 'precompiler', 'dart2js', 'dart2analyzer'],
+              ['none', 'precompiler', 'dart2js', 'dart2analyzer',
+               'dart2snapshot'],
               'none'),
           // TODO(antonm): fix the option drt.
           new _TestOptionSpecification(
@@ -78,6 +82,8 @@ class TestOptionsParser {
     dart_precompiled: Run a precompiled snapshot on a variant of the standalone
                       dart vm lacking a JIT.
 
+    dart_snapshotted: Run a full snapshot.
+
     d8: Run JavaScript from the command line using v8.
 
     jsshell: Run JavaScript from the command line using firefox js-shell.
@@ -98,7 +104,8 @@ class TestOptionsParser {
     none: No runtime, compile only (for example, used for dart2analyzer static
           analysis tests).''',
               ['-r', '--runtime'],
-              ['vm', 'dart_precompiled', 'd8', 'jsshell', 'drt', 'dartium',
+              ['vm', 'dart_precompiled', 'dart_snapshotted',
+               'd8', 'jsshell', 'drt', 'dartium',
                'ff', 'firefox',
                'chrome', 'safari', 'ie9', 'ie10', 'ie11', 'opera',
                'chromeOnAndroid', 'safarimobilesim',
@@ -648,6 +655,9 @@ Note: currently only implemented for dart2js.''',
       case 'dart2analyzer':
         validRuntimes = const ['none'];
         break;
+      case 'dart2snapshot':
+        validRuntimes = const ['dart_snapshotted'];
+        break;
       case 'precompiler':
         validRuntimes = const ['dart_precompiled'];
         break;