fix code completion when enableTrailingCommas is true

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

Index: pkg/analysis_server/test/services/completion/completion_target_test.dart
diff --git a/pkg/analysis_server/test/services/completion/completion_target_test.dart b/pkg/analysis_server/test/services/completion/completion_target_test.dart
index 569610cb219a389cc2efefe22474971a913bf8f2..f7cca21b8d96b746e60d1a52e2c137b1636da2d7 100644
--- a/pkg/analysis_server/test/services/completion/completion_target_test.dart
+++ b/pkg/analysis_server/test/services/completion/completion_target_test.dart
@@ -61,6 +61,16 @@ class CompletionTargetTest extends AbstractContextTest {
     assertTarget(')', '()', argIndex: 0);
   }
 
+  test_ArgumentList_InstanceCreationExpression2() {
+    // ArgumentList  InstanceCreationExpression  Block
+    addTestSource('main() {new Foo(a,^)}');
+    if (context.analysisOptions.enableTrailingCommas) {
+      assertTarget(')', '(a)', argIndex: 1);
+    } else {
+      assertTarget('', '(a, )', argIndex: 1);
+    }
+  }
+
   test_ArgumentList_InstanceCreationExpression_functionArg2() {
     // ArgumentList  InstanceCreationExpression  Block
     addTestSource('main() {new B(^)} class B{B(f()){}}');
@@ -85,10 +95,20 @@ class CompletionTargetTest extends AbstractContextTest {
     assertTarget('n', '(n)', argIndex: 0);
   }
 
+  test_ArgumentList_MethodInvocation3a() {
+    // ArgumentList  MethodInvocation  Block
+    addTestSource('main() {foo((n)^)}');
+    assertTarget(')', '((n))', argIndex: 0);
+  }
+
   test_ArgumentList_MethodInvocation4() {
     // ArgumentList  MethodInvocation  Block
     addTestSource('main() {foo(n,^)}');
-    assertTarget('', '(n, )', argIndex: 1);
+    if (context.analysisOptions.enableTrailingCommas) {
+      assertTarget(')', '(n)', argIndex: 1);
+    } else {
+      assertTarget('', '(n, )', argIndex: 1);
+    }
   }
 
   test_ArgumentList_MethodInvocation_functionArg() {