Use the polling watcher by default in pub tests for now.

sdk/lib/_internal/pub/lib/src/command/build.dart

Index: sdk/lib/_internal/pub/lib/src/command/build.dart
diff --git a/sdk/lib/_internal/pub/lib/src/command/build.dart b/sdk/lib/_internal/pub/lib/src/command/build.dart
index 12dccf072c4d18ed0a85413d12f3ad74338a91e6..4cacb6d310069c49ee5b068e0a2eff7abf3ef10f 100644
--- a/sdk/lib/_internal/pub/lib/src/command/build.dart
+++ b/sdk/lib/_internal/pub/lib/src/command/build.dart
@@ -61,7 +61,7 @@ class BuildCommand extends PubCommand {
       // TODO(rnystrom): Allow specifying mode.
       return barback.createServer("127.0.0.1", 0, graph, BarbackMode.RELEASE,
           builtInTransformers: [dart2jsTransformer],
-          watchForUpdates: false);
+          watcher: barback.WatcherType.NONE);
     }).then((server) {
       // Show in-progress errors, but not results. Those get handled implicitly
       // by getAllAssets().