Revise barback logging patch.

sdk/lib/_internal/pub/lib/src/barback/dart2js_transformer.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library pub.dart2js_transformer;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:analyzer/analyzer.dart';
@@ skipping 61 matching lines @@
       var packageRoot = path.join(_graph.entrypoint.root.dir, "packages");
 
       // TODO(rnystrom): Should have more sophisticated error-handling here.
       // Need to report compile errors to the user in an easily visible way.
       // Need to make sure paths in errors are mapped to the original source
       // path so they can understand them.
       return dart.compile(entrypoint,
           packageRoot: packageRoot,
           inputProvider: provider.readStringFromUri,
           diagnosticHandler: provider.handleDiagnostic).then((js) {
-        if (js == null) {
-          // The compile failed and errors should have already been reported
-          // through the diagnostic handler, so just do nothing here.
-          return;
-        }
-
         var id = transform.primaryInput.id.changeExtension(".dart.js");
         transform.addOutput(new Asset.fromString(id, js));
 
         stopwatch.stop();
         transform.logger.info("Generated $id (${js.length} characters) in "
             "${stopwatch.elapsed}");
+      }).catchError((error) {
+        // The compile failed and errors have been reported through the
+        // diagnostic handler, so just do nothing here.
+        if (error is CompilerException) return;
+        throw error;
       });
     });
   }
 }
 
 /// Defines methods implementig [CompilerInputProvider] and [DiagnosticHandler]
 /// for dart2js to use to load files from Barback and report errors.
 ///
 /// Note that most of the implementation of diagnostic handling here was
 /// copied from [FormattingDiagnosticHandler] in dart2js. The primary
@@ skipping 134 matching lines @@
     var rootDir = _graph.entrypoint.root.dir;
     var sourcePath = path.fromUri(url);
     if (isBeneath(sourcePath, rootDir)) {
       var relative = path.relative(sourcePath, from: rootDir);
       return new AssetId(_graph.entrypoint.root.name, relative);
     }
 
     return null;
   }
 }