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

pkg/analyzer/test/generated/element_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.element_test;
 
 import 'package:analyzer/src/generated/java_core.dart';
@@ skipping 110 matching lines @@
     ClassElementImpl classA = ElementFactory.classElement2("A", []);
     String methodName = "m";
     MethodElement method = ElementFactory.methodElement(methodName, null, []);
     classA.methods = <MethodElement> [method];
     JUnitTestCase.assertNull(classA.getMethod("${methodName}x"));
   }
 
   void test_getNode() {
     AnalysisContextHelper contextHelper = new AnalysisContextHelper();
     AnalysisContext context = contextHelper.context;
-    Source source = contextHelper.addSource("/test.dart", EngineTestCase.createSource(["class A {}", "class B {}"]));
+    Source source = contextHelper.addSource("/test.dart", r'''
+class A {}
+class B {}''');
     // prepare CompilationUnitElement
     LibraryElement libraryElement = context.computeLibraryElement(source);
     CompilationUnitElement unitElement = libraryElement.definingCompilationUnit;
     // A
     {
       ClassElement elementA = unitElement.getType("A");
       ClassDeclaration nodeA = elementA.node;
       JUnitTestCase.assertNotNull(nodeA);
       JUnitTestCase.assertEquals("A", nodeA.name.name);
       JUnitTestCase.assertSame(elementA, nodeA.element);
@@ skipping 3336 matching lines @@
   runReflectiveTests(UnionTypeImplTest);
   runReflectiveTests(VoidTypeImplTest);
   runReflectiveTests(ClassElementImplTest);
   runReflectiveTests(CompilationUnitElementImplTest);
   runReflectiveTests(ElementLocationImplTest);
   runReflectiveTests(ElementImplTest);
   runReflectiveTests(HtmlElementImplTest);
   runReflectiveTests(LibraryElementImplTest);
   runReflectiveTests(MultiplyDefinedElementImplTest);
 }