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

pkg/analyzer/test/generated/test_support.dart

Index: pkg/analyzer/test/generated/test_support.dart
diff --git a/pkg/analyzer/test/generated/test_support.dart b/pkg/analyzer/test/generated/test_support.dart
index a31920983b039f9d1b39d2c54e7322ee977b799d..ebcac9193256601851be9c224604e01e84c89f7c 100644
--- a/pkg/analyzer/test/generated/test_support.dart
+++ b/pkg/analyzer/test/generated/test_support.dart
@@ -438,7 +438,7 @@ class EngineTestCase extends JUnitTestCase {
       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);