Don't monitor the filesystem during "pub build".

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 04d8ea61d13e60496bafb08455636a0dd922950c..4805c0a0e3eabb7513545c9ad6a389ac33af259c 100644
--- a/sdk/lib/_internal/pub/lib/src/command/build.dart
+++ b/sdk/lib/_internal/pub/lib/src/command/build.dart
@@ -51,7 +51,8 @@ class BuildCommand extends PubCommand {
       // user-facing, just use an IPv4 address to avoid a weird bug on the
       // OS X buildbots.
       return barback.createServer("127.0.0.1", 0, graph,
-          builtInTransformers: [dart2jsTransformer]);
+          builtInTransformers: [dart2jsTransformer],
+          watchForUpdates: false);
     }).then((server) {
       // Show in-progress errors, but not results. Those get handled implicitly
       // by getAllAssets().