Create a NullErrorReporter to use when errors don't need to be recorded.

pkg/analyzer/lib/src/generated/error.dart

Index: pkg/analyzer/lib/src/generated/error.dart
diff --git a/pkg/analyzer/lib/src/generated/error.dart b/pkg/analyzer/lib/src/generated/error.dart
index 1d5beba66fd7413f8b91e4e210c83b7cb032f8de..9643ccdb67d4aa5cd6b3d212cb221baa3606009d 100644
--- a/pkg/analyzer/lib/src/generated/error.dart
+++ b/pkg/analyzer/lib/src/generated/error.dart
@@ -2775,6 +2775,16 @@ class HtmlWarningCode extends Enum<HtmlWarningCode> implements ErrorCode {
 }
 
 /**
+ * Instances of the class `NullErrorListener` implement the
+ * AnalysisErrorListener interface, but don't record any information.
+ */
+class NullErrorListener implements AnalysisErrorListener {

[Brian Wilkerson, 2014/10/06 16:49:41]

Or use the poorly named but existing class
AnalysisErrorListener_NULL_LISTENER...

[Paul Berry, 2014/10/06 16:56:52]

Done.

+  @override
+  void onError(AnalysisError error) {
+  }
+}
+
+/**
  * The enumeration `PolymerCode` defines Polymer specific problems.
  */
 class PolymerCode extends Enum<PolymerCode> implements ErrorCode {