Check in codegen test expectations.

test/codegen/expect/corelib/string_source_test.js

Index: test/codegen/expect/corelib/string_source_test.js
diff --git a/test/codegen/expect/corelib/string_source_test.js b/test/codegen/expect/corelib/string_source_test.js
new file mode 100644
index 0000000000000000000000000000000000000000..39e4170b96159191e137f7e70a9b1b15ca0640ca
--- /dev/null
+++ b/test/codegen/expect/corelib/string_source_test.js
@@ -0,0 +1,38 @@
+dart_library.library('corelib/string_source_test', null, /* Imports */[
+  'dart_sdk',
+  'expect'
+], function load__string_source_test(exports, dart_sdk, expect) {
+  'use strict';
+  const core = dart_sdk.core;
+  const _interceptors = dart_sdk._interceptors;
+  const convert = dart_sdk.convert;
+  const dart = dart_sdk.dart;
+  const dartx = dart_sdk.dartx;
+  const expect$ = expect.expect;
+  const string_source_test = Object.create(null);
+  let JSArrayOfint = () => (JSArrayOfint = dart.constFn(_interceptors.JSArray$(core.int)))();
+  let VoidTodynamic = () => (VoidTodynamic = dart.constFn(dart.definiteFunctionType(dart.dynamic, [])))();
+  string_source_test.main = function() {
+    let base = "𐐒";
+    let strings = ["𐐒", "𐐒", core.String.fromCharCodes(JSArrayOfint().of([55297, 56338])), dart.notNull(base[dartx.get](0)) + dart.notNull(base[dartx.get](1)), dart.str`${base}`, dart.str`${base[dartx.get](0)}${base[dartx.get](1)}`, dart.str`${base[dartx.get](0)}${base[dartx.substring](1)}`, core.String.fromCharCodes(JSArrayOfint().of([66578])), ("a" + base)[dartx.substring](1), (() => {
+        let _ = new core.StringBuffer();
+        _.writeCharCode(55297);
+        _.writeCharCode(56338);
+        return _;
+      })().toString(), (() => {
+        let _ = new core.StringBuffer();
+        _.writeCharCode(66578);
+        return _;
+      })().toString(), convert.JSON.decode('"𐐒"'), core.Map.as(convert.JSON.decode('{"𐐒":[]}'))[dartx.keys][dartx.first]];
+    for (let string of strings) {
+      core.String._check(string);
+      expect$.Expect.equals(base[dartx.length], string[dartx.length]);
+      expect$.Expect.equals(base, string);
+      expect$.Expect.equals(dart.hashCode(base), dart.hashCode(string));
+      expect$.Expect.listEquals(base[dartx.codeUnits][dartx.toList](), string[dartx.codeUnits][dartx.toList]());
+    }
+  };
+  dart.fn(string_source_test.main, VoidTodynamic());
+  // Exports:
+  exports.string_source_test = string_source_test;
+});