Suppress some polymer runtime warnings.

runtime/bin/vmservice/client/web/main.dart

Index: runtime/bin/vmservice/client/web/main.dart
diff --git a/runtime/bin/vmservice/client/web/main.dart b/runtime/bin/vmservice/client/web/main.dart
index f3865298eebcb7253e018e0efd39045d2cbacdaa..db5153ceb9803579d5be5e462ce89db09a3c4d8c 100644
--- a/runtime/bin/vmservice/client/web/main.dart
+++ b/runtime/bin/vmservice/client/web/main.dart
@@ -9,7 +9,14 @@ import 'package:polymer/polymer.dart';
 main() {
   Logger.root.level = Level.INFO;
   Logger.root.onRecord.listen((LogRecord rec) {
-    print('${rec.level.name}: ${rec.time}: ${rec.message}');
+      if (rec.level == Level.WARNING &&
+          rec.message.startsWith('Error evaluating expression') &&
+          (rec.message.contains("Can't assign to null: ") ||
+           rec.message.contains('Expression is not assignable: '))) {
+        // Suppress flaky polymer errors.
+        return;
+      }
+      print('${rec.level.name}: ${rec.time}: ${rec.message}');
   });
   Logger.root.info('Starting Observatory');
   GoogleChart.initOnce().then((_) {
@@ -17,4 +24,4 @@ main() {
     Logger.root.info('Initializing Polymer');
     initPolymer();
   });
-}
+}