Extract appending nodes to the list into a helper method.

pkg/analyzer/lib/src/dart/sdk/patch.dart

Index: pkg/analyzer/lib/src/dart/sdk/patch.dart
diff --git a/pkg/analyzer/lib/src/dart/sdk/patch.dart b/pkg/analyzer/lib/src/dart/sdk/patch.dart
index e6475c3a028e7ae4d5f37be559c2967e5563eabe..02b497cf392cb33b32b80bc76bf7b56c4ded717c 100644
--- a/pkg/analyzer/lib/src/dart/sdk/patch.dart
+++ b/pkg/analyzer/lib/src/dart/sdk/patch.dart
@@ -197,14 +197,9 @@ class SdkPatcher {
             patchMember.offset);
       }
     }
-    // Append new top-level declarations.
-    Token lastToken = baseClass.endToken.previous;
-    for (ClassMember newMember in membersToAppend) {
-      newMember.endToken.setNext(lastToken.next);
-      lastToken.setNext(newMember.beginToken);
-      baseClass.members.add(newMember);
-      lastToken = newMember.endToken;
-    }
+    // Append new class members.
+    _appendToNodeList(
+        baseClass.members, membersToAppend, baseClass.leftBracket);
   }
 
   void _patchDirectives(
@@ -279,13 +274,8 @@ class SdkPatcher {
       }
     }
     // Append new top-level declarations.
-    Token lastToken = baseUnit.endToken.previous;
-    for (CompilationUnitMember newDeclaration in declarationsToAppend) {
-      newDeclaration.endToken.setNext(lastToken.next);
-      lastToken.setNext(newDeclaration.beginToken);
-      baseUnit.declarations.add(newDeclaration);
-      lastToken = newDeclaration.endToken;
-    }
+    _appendToNodeList(baseUnit.declarations, declarationsToAppend,
+        baseUnit.endToken.previous);
   }
 
   /**
@@ -310,6 +300,21 @@ class SdkPatcher {
   }
 
   /**
+   * Append [newNodes] to the given [nodes] and attach new tokens to the end
+   * token of the last [nodes] items, or, if it is empty, to [defaultPrevToken].
+   */
+  static void _appendToNodeList(
+      NodeList<AstNode> nodes, List<AstNode> newNodes, Token defaultPrevToken) {
+    Token prevToken = nodes.endToken ?? defaultPrevToken;
+    for (AstNode newNode in newNodes) {
+      newNode.endToken.setNext(prevToken.next);
+      prevToken.setNext(newNode.beginToken);
+      nodes.add(newNode);
+      prevToken = newNode.endToken;
+    }
+  }
+
+  /**
    * Return `true` if [metadata] has the `@patch` annotation.
    */
   static bool _hasPatchAnnotation(List<Annotation> metadata) {