Convert most of the EngineTestCase.createSource invocations into multi-line String literals.

pkg/analyzer/test/generated/scanner_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.
 
 // This code was auto-generated, is not intended to be edited, and is subject to
 // significant change. Please see the README file for more information.
 
 library engine.scanner_test;
 
 import 'package:analyzer/src/generated/java_core.dart';
@@ skipping 252 matching lines @@
     // "a + b; "
     // "a + b;  "
     _scan("a + b; ", "", " ", "");
     _assertTokens(3, 4, ["a", "+", "b", ";"]);
     JUnitTestCase.assertFalse(_incrementalScanner.hasNonWhitespaceChange);
   }
 
   void test_insert_whitespace_withMultipleComments() {
     // "//comment", "//comment2", "a + b;"
     // "//comment", "//comment2", "a  + b;"
-    _scan(EngineTestCase.createSource(["//comment", "//comment2", "a"]), "", " ", " + b;");
+    _scan(r'''
+//comment
+//comment2
+a''', "", " ", " + b;");
     _assertTokens(1, 2, ["a", "+", "b", ";"]);
     JUnitTestCase.assertFalse(_incrementalScanner.hasNonWhitespaceChange);
   }
 
   void test_replace_identifier_beginning() {
     // "bell + b;"
     // "fell + b;")
     _scan("", "b", "f", "ell + b;");
     _assertTokens(-1, 1, ["fell", "+", "b", ";"]);
     JUnitTestCase.assertTrue(_incrementalScanner.hasNonWhitespaceChange);
@@ skipping 1350 matching lines @@
 }
 
 main() {
   _ut.groupSep = ' | ';
   runReflectiveTests(CharSequenceReaderTest);
   runReflectiveTests(IncrementalScannerTest);
   runReflectiveTests(KeywordStateTest);
   runReflectiveTests(ScannerTest);
   runReflectiveTests(TokenTypeTest);
 }