Link to stable-errors site from pub-build messages on the command line.

pkg/polymer/test/build/common.dart

Index: pkg/polymer/test/build/common.dart
diff --git a/pkg/polymer/test/build/common.dart b/pkg/polymer/test/build/common.dart
index 13411e66eda9801c2895eba5e736b1eb733f0437..c50efa64db18d370ac0bcffb82769eaa06420722 100644
--- a/pkg/polymer/test/build/common.dart
+++ b/pkg/polymer/test/build/common.dart
@@ -74,7 +74,12 @@ class TestHelper implements PackageProvider {
       // We only check messages when an expectation is provided.
       if (messages == null) return;
 
-      var msg = '${entry.level.name.toLowerCase()}: ${entry.message}';
+      var errorLink = new RegExp(
+          ' See http://goo.gl/5HPeuP#polymer_[0-9]* for details.');
+      var text = entry.message;
+      var newText = text.replaceFirst(errorLink, '');
+      expect(text != newText, isTrue);
+      var msg = '${entry.level.name.toLowerCase()}: ${newText}';
       var span = entry.span;
       var spanInfo = span == null ? '' :
           ' (${span.sourceUrl} ${span.start.line} ${span.start.column})';