In test.dart, don't check that the shell or compiler executable exists if we are just listing tests.

tools/testing/dart/test_suite.dart

Index: tools/testing/dart/test_suite.dart
diff --git a/tools/testing/dart/test_suite.dart b/tools/testing/dart/test_suite.dart
index 1b0fe024f683a395be35f3670a19cd4dc23543dc..47738b8107418c1c8c0a59951b58894f9d0d600a 100644
--- a/tools/testing/dart/test_suite.dart
+++ b/tools/testing/dart/test_suite.dart
@@ -964,7 +964,7 @@ class TestUtils {
 
   static String dartShellFileName(Map configuration) {
     var name = '${buildDir(configuration)}/${executableName(configuration)}';
-    if (!(new File(name)).existsSync()) {
+    if (!(new File(name)).existsSync() && !configuration['list']) {
       throw "Executable '$name' does not exist";
     }
     return name;
@@ -978,7 +978,7 @@ class TestUtils {
     if (name == '') {
       name = '${buildDir(configuration)}/${compilerName(configuration)}';
     }
-    if (!(new File(name)).existsSync()) {
+    if (!(new File(name)).existsSync() && !configuration['list']) {
       throw "Executable '$name' does not exist";
     }
     return name;