Fix warnings in dart2js and analyzer caused by Fasta.

pkg/analyzer/lib/src/fasta/mock_element.dart

Index: pkg/analyzer/lib/src/fasta/mock_element.dart
diff --git a/pkg/analyzer/lib/src/fasta/mock_element.dart b/pkg/analyzer/lib/src/fasta/mock_element.dart
index 137756c0894342ee81feaf0320879e62e4aa05bf..f4404ae775c59553c7519edd9ac8bd43e4ba7fb8 100644
--- a/pkg/analyzer/lib/src/fasta/mock_element.dart
+++ b/pkg/analyzer/lib/src/fasta/mock_element.dart
@@ -58,6 +58,8 @@ abstract class MockElement extends Builder implements Element, LocalElement {
 
   String get name => internalError("not supported.");
 
+  String get fullNameForErrors => name;
+
   int get nameLength => internalError("not supported.");
 
   int get nameOffset => -1;