Update some of the fixes to use ChangeBuilder

pkg/analyzer_plugin/lib/src/utilities/change_builder/change_builder_dart.dart

 // Copyright (c) 2017, 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.
 
 import 'dart:async';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
@@ skipping 1013 matching lines @@
     InterfaceType futureType = typeProvider.futureType;
     //
     // Check whether the type needs to be replaced.
     //
     DartType type = typeAnnotation?.type;
     if (type == null ||
         type.isDynamic ||
         type is InterfaceType && type.element == futureType.element) {
       return;
     }
-    futureType = futureType.instantiate(<DartType>[type]);
+    // TODO(brianwilkerson) Unconditionally execute the body of the 'if' when
+    // Future<void> is fully supported.
+    if (!type.isVoid) {
+      futureType = futureType.instantiate(<DartType>[type]);
+    }
     // prepare code for the types
     addReplacement(range.node(typeAnnotation), (EditBuilder builder) {
       if (!(builder as DartEditBuilder).writeType(futureType)) {
         builder.write('void');
       }
     });
   }
 
   /**
    * Adds edits to the given [change] that ensure that all the [libraries] are
@@ skipping 90 matching lines @@
         builder.write(importUri);
         builder.writeln("';");
         if (i == uriList.length - 1 && desc.insertEmptyLineAfter) {
           builder.writeln();
         }
       });
     }
   }
 
   /**
-   * Returns a [InsertDesc] describing where to insert a new directive or a
-   * top-level declaration at the top of the file.
+   * Returns an insertion description describing where to insert a new directive
+   * or a top-level declaration at the top of the file.
    */
   _InsertionDescription _getInsertDescTop() {
     // skip leading line comments
     int offset = 0;
     bool insertEmptyLineBefore = false;
     bool insertEmptyLineAfter = false;
     String source = unit.element.context.getContents(unit.element.source).data;
     var lineInfo = unit.lineInfo;
     // skip hash-bang
     if (offset < source.length - 2) {
@@ skipping 23 matching lines @@
       String linePrefix = _getText(source, offset, 2);
       if (linePrefix == "//") {
         insertEmptyLineBefore = true;
         offset = lineInfo.getOffsetOfLineAfter(offset);
       } else {
         break;
       }
     }
     // determine if empty line is required after
     int currentLine = lineInfo.getLocation(offset).lineNumber;
-    if (currentLine < lineInfo.lineCount) {
+    if (currentLine + 1 < lineInfo.lineCount) {
       int nextLineOffset = lineInfo.getOffsetOfLine(currentLine + 1);
       String insertLine = source.substring(offset, nextLineOffset);
       if (!insertLine.trim().isEmpty) {
         insertEmptyLineAfter = true;
       }
     }
     return new _InsertionDescription(
         offset, insertEmptyLineBefore, insertEmptyLineAfter);
   }
 
@@ skipping 125 matching lines @@
   }
 }
 
 class _InsertionDescription {
   final int offset;
   final bool insertEmptyLineBefore;
   final bool insertEmptyLineAfter;
   _InsertionDescription(
       this.offset, this.insertEmptyLineBefore, this.insertEmptyLineAfter);
 }