Include dart/test_all into src/test_all and fix element tests.

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

Index: pkg/analyzer/lib/src/generated/source.dart
diff --git a/pkg/analyzer/lib/src/generated/source.dart b/pkg/analyzer/lib/src/generated/source.dart
index c9d1b45617c0f3a38b95af180dc1a99b1c904f53..8fcdad35bcaffd036ad16837b0a42d224121bdc0 100644
--- a/pkg/analyzer/lib/src/generated/source.dart
+++ b/pkg/analyzer/lib/src/generated/source.dart
@@ -379,9 +379,7 @@ class NonExistingSource extends Source {
   }
 
   @override
-  String get encoding {
-    throw new UnsupportedOperationException('$fullName does not exist.');
-  }
+  String get encoding => uri.toString();
 
   @override
   int get hashCode => fullName.hashCode;