improve parser recovery for incomplete prefixed identifier in method/function parameter list

pkg/analysis_server/test/services/completion/completion_test_util.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library test.services.completion.util;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/protocol.dart' as protocol
     show Element, ElementKind;
@@ skipping 3247 matching lines @@
       assertSuggestInvocationClass('Y');
       assertNotSuggested('T1');
       assertNotSuggested('T2');
       assertNotSuggested('Object');
       assertNotSuggested('b');
       assertNotSuggested('A');
       assertNotSuggested('==');
     });
   }
 
+  test_PrefixedIdentifier_library_typesOnly2() {
+    // SimpleIdentifier  PrefixedIdentifier  TypeName
+    addSource('/testB.dart', '''
+      lib B;
+      var T1;
+      class X { }
+      class Y { }''');
+    addTestSource('''
+      import "/testB.dart" as b;
+      var T2;
+      class A { }
+      foo(b.^) {}''');
+    computeFast();
+    return computeFull((bool result) {
+      expect(request.replacementOffset, completionOffset);
+      expect(request.replacementLength, 0);
+      assertSuggestInvocationClass('X');
+      assertSuggestInvocationClass('Y');
+      assertNotSuggested('T1');
+      assertNotSuggested('T2');
+      assertNotSuggested('Object');
+      assertNotSuggested('b');
+      assertNotSuggested('A');
+      assertNotSuggested('==');
+    });
+  }
+
   test_PrefixedIdentifier_parameter() {
     // SimpleIdentifier  PrefixedIdentifier  ExpressionStatement
     addSource('/testB.dart', '''
       lib B;
       class _W {M y; var _z;}
       class X extends _W {}
       class M{}''');
     addTestSource('''
       import "/testB.dart";
       foo(X x) {x.^}''');
@@ skipping 404 matching lines @@
       assertNotSuggested('bar2');
       assertNotSuggested('_B');
       assertSuggestLocalClass('Y');
       assertSuggestLocalClass('C');
       assertSuggestLocalVariable('f', null);
       assertNotSuggested('x');
       assertNotSuggested('e');
     });
   }
 }