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

pkg/analyzer/test/generated/test_support.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.test_support;
 
 import 'dart:collection';
@@ skipping 420 matching lines @@
     return writer.toString();
   }
 
   /**
    * @return the [AstNode] with requested type at offset of the "prefix".
    */
   static AstNode findNode(AstNode root, String code, String prefix,
       Predicate<AstNode> predicate) {
     int offset = code.indexOf(prefix);
     if (offset == -1) {
-      throw new IllegalArgumentException("Not found '${prefix}'.");
+      throw new IllegalArgumentException("Not found '$prefix'.");
     }
     AstNode node = new NodeLocator.con1(offset).searchWithin(root);
     return node.getAncestor(predicate);
   }
 
   /**
    * Calculate the offset where the given strings differ.
    *
    * @param str1 the first String to compare
    * @param str2 the second String to compare
@@ skipping 553 matching lines @@
   void getContentsToReceiver(Source_ContentReceiver receiver) {
     throw new UnsupportedOperationException();
   }
   Source resolve(String uri) {
     throw new UnsupportedOperationException();
   }
   Uri resolveRelativeUri(Uri uri) {
     return new Uri(scheme: 'file', path: _name).resolveUri(uri);
   }
 }