Fix build (#11186)

Was broken by https://github.com/flutter/flutter/commit/dba29aa0fce684b201c6b03efc73ba607c7b507b, which apprently has been pushed directly to master without running through Travis?

packages/flutter_tools/lib/src/dart/dependencies.dart

@@ -15,7 +15,7 @@ final List<String> _configurationConstants = <String>['dart.library.io'];
 
 String _dottedNameToString(analyzer.DottedName dottedName) {
   String result = '';
-  for (var identifier in dottedName.components) {
+  for (analyzer.SimpleIdentifier identifier in dottedName.components) {
     if (result.isEmpty) {
       result += identifier.token.lexeme;
     } else {