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

pkg/analysis_server/test/services/completion/completion_target_test.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.target;
 
 import 'package:analysis_server/src/services/completion/completion_target.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:unittest/unittest.dart';
@@ skipping 120 matching lines @@
     addTestSource('class A {var b; X _c; foo() {var a; (a as ^String).foo();}');
     assertTarget('String', 'a as String');
   }
 
   test_Block() {
     // Block
     addTestSource('main() {^}');
     assertTarget('}', '{}');
   }
 
+  test_FormalParameter_partialType() {
+    // SimpleIdentifier  PrefixedIdentifier  TypeName
+    addTestSource('foo(b.^ f) { }');
+    assertTarget('f', 'b.f');
+  }
+
+  test_FormalParameter_partialType2() {
+    // SimpleIdentifier  PrefixedIdentifier  TypeName
+    addTestSource('foo(b.z^ f) { }');
+    assertTarget('z', 'b.z');
+  }
+
+  test_FormalParameter_partialType3() {
+    // SimpleIdentifier  PrefixedIdentifier  TypeName
+    addTestSource('foo(b.^) { }');
+    assertTarget('', 'b.');
+  }
+
+  test_FormalParameterList() {
+    // Token  FormalParameterList  FunctionExpression
+    addTestSource('foo(^) { }');
+    assertTarget(')', '()');
+  }
+
   test_FunctionDeclaration_inLineComment() {
     // Comment  CompilationUnit
     addTestSource('''
       // normal comment ^
       zoo(z) { } String name;''');
     assertTarget('// normal comment ', 'zoo(z) {} String name;');
   }
 
   test_FunctionDeclaration_inLineComment2() {
     // Comment  CompilationUnit
@@ skipping 340 matching lines @@
     addTestSource('main() {int b^ = 1;}');
     assertTarget('b = 1', 'int b = 1');
   }
 
   test_VariableDeclaration_lhs_identifier_before() {
     // VariableDeclaration  VariableDeclarationList
     addTestSource('main() {int ^b = 1;}');
     assertTarget('b = 1', 'int b = 1');
   }
 }