Dart 2 fixes in the gardening tools

Change-Id: Ib6339d20a15eb340aedb242f2c228dc2aeaac8b3
Reviewed-on: https://dart-review.googlesource.com/63341
Reviewed-by: Bob Nystrom <rnystrom@google.com>
Commit-Queue: Leaf Petersen <leafp@google.com>
diff --git a/tools/gardening/lib/src/results/failing_test.dart b/tools/gardening/lib/src/results/failing_test.dart
index e19a1e3..e8ff1f1 100644
--- a/tools/gardening/lib/src/results/failing_test.dart
+++ b/tools/gardening/lib/src/results/failing_test.dart
@@ -83,7 +83,7 @@
     var entries = _sectionEntriesForTestInConfigurations(
         expectations, failingConfigurations, result.name,
         success: false);
-    return new Set.from(entries).toList();
+    return new Set.of(entries).toList();
   }
 
   /// Gets the failing configurations not covered by expressions in [sections].
diff --git a/tools/gardening/lib/src/results/result_json_models.dart b/tools/gardening/lib/src/results/result_json_models.dart
index 1e3a0da..287902d 100644
--- a/tools/gardening/lib/src/results/result_json_models.dart
+++ b/tools/gardening/lib/src/results/result_json_models.dart
@@ -130,7 +130,7 @@
   }
 
   String _boolToArg(String name, bool value) {
-    return value ? "--$name" : null;
+    return value == true ? "--$name" : null;
   }
 
   String _listToArg(String name, List<String> strings) {