Revise barback logging patch.

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

Index: sdk/lib/_internal/pub/lib/src/dart.dart
diff --git a/sdk/lib/_internal/pub/lib/src/dart.dart b/sdk/lib/_internal/pub/lib/src/dart.dart
index e0701a4bffa47dbdbc5d40a13175c3c667ea725a..d183f37e40cbbb65c7ad70aaee6c19ad210af186 100644
--- a/sdk/lib/_internal/pub/lib/src/dart.dart
+++ b/sdk/lib/_internal/pub/lib/src/dart.dart
@@ -57,7 +57,10 @@ Future<String> compile(String entrypoint, {String packageRoot,
         path.toUri(entrypoint),
         path.toUri(appendSlash(_libPath)),
         path.toUri(appendSlash(packageRoot)),
-        inputProvider, diagnosticHandler, options);
+        inputProvider, diagnosticHandler, options).then((js) {
+      if (js == null) throw new CompilerException(entrypoint);
+      return js;
+    });
   });
 }
 
@@ -175,3 +178,9 @@ class CrossIsolateException implements Exception {
 
   String toString() => "$message\n$stackTrace";
 }
+
+/// An exception thrown when dart2js generates compiler errors.
+class CompilerException extends ApplicationException {
+  CompilerException(String entrypoint)
+      : super('Failed to compile "$entrypoint".');
+}