Wait for all log entries to be printed before exiting "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 b13e4d8bdb103e845d4df4542bb50b833ee19473..80d1ec7665ee9229183468825e20a2a007cc212b 100644
--- a/sdk/lib/_internal/pub/lib/src/command/build.dart
+++ b/sdk/lib/_internal/pub/lib/src/command/build.dart
@@ -73,8 +73,9 @@ class BuildCommand extends PubCommand {
         log.error(log.red("Build error:\n$error"));
       });
 
-      return log.progress("Building ${entrypoint.root.name}",
-          () => server.barback.getAllAssets());
+      return log.progress("Building ${entrypoint.root.name}", () {
+        return server.barback.getAllAssets();
+      });
     }).then((assets) {
       return Future.wait(assets.map((asset) {
         // In release mode, strip out .dart files since all relevant ones have