Print "Building $app..." before any transformers start running.

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 d7a6e8ee1556dbd64ed514d2f7e2b306aada7d0d..2513d8b990021a7a46c07b7cce8c75f2f7dad560 100644
--- a/sdk/lib/_internal/pub/lib/src/command/build.dart
+++ b/sdk/lib/_internal/pub/lib/src/command/build.dart
@@ -62,7 +62,6 @@ class BuildCommand extends PubCommand {
     _parseBuildDirectories();
     cleanDir(target);
 
-    var environment;
     var errorsJson = [];
     var logJson = [];
 
@@ -71,24 +70,15 @@ class BuildCommand extends PubCommand {
     // OS X buildbots.
     return BuildEnvironment.create(entrypoint, "127.0.0.1", 0, mode,
         WatcherType.NONE, useDart2JS: true)
-          .then((env) {
-      environment = env;
-
-      // Register all of the build directories.
-      // TODO(rnystrom): We don't actually need to bind servers for these, we
-      // just need to add them to barback's sources. Add support to
-      // BuildEnvironment for going the latter without the former.
-      return Future.wait(buildDirectories.map(
-          (dir) => environment.serveDirectory(dir)));
-    }).then((_) {
-      // Show in-progress errors, but not results. Those get handled implicitly
-      // by getAllAssets().
+          .then((environment) {
+      // Show in-progress errors, but not results. Those get handled
+      // implicitly by getAllAssets().
       environment.barback.errors.listen((error) {
         log.error(log.red("Build error:\n$error"));
 
         if (log.json.enabled) {
-          // Wrap the error in a map in case we end up decorating it with more
-          // properties later.
+          // Wrap the error in a map in case we end up decorating it with
+          // more properties later.
           errorsJson.add({
             "error": error.toString()
           });
@@ -102,8 +92,17 @@ class BuildCommand extends PubCommand {
             (entry) => logJson.add(_logEntryToJson(entry)));
       }
 
-      return log.progress("Building ${entrypoint.root.name}",
-          () => environment.barback.getAllAssets()).then((assets) {
+      return log.progress("Building ${entrypoint.root.name}", () {
+        // Register all of the build directories.
+        // TODO(rnystrom): We don't actually need to bind servers for these, we
+        // just need to add them to barback's sources. Add support to
+        // BuildEnvironment for going the latter without the former.
+        return Future.wait(buildDirectories.map(
+            (dir) => environment.serveDirectory(dir))).then((_) {
+
+          return environment.barback.getAllAssets();
+        });
+      }).then((assets) {
         // Find all of the JS entrypoints we built.
         var dart2JSEntrypoints = assets
             .where((asset) => asset.id.path.endsWith(".dart.js"))