Check in codegen test expectations.

test/codegen/expect/corelib/string_trim_test.js

Index: test/codegen/expect/corelib/string_trim_test.js
diff --git a/test/codegen/expect/corelib/string_trim_test.js b/test/codegen/expect/corelib/string_trim_test.js
new file mode 100644
index 0000000000000000000000000000000000000000..d55856fbfe01305a0e09dcb6d0192732e31c8f41
--- /dev/null
+++ b/test/codegen/expect/corelib/string_trim_test.js
@@ -0,0 +1,37 @@
+dart_library.library('corelib/string_trim_test', null, /* Imports */[
+  'dart_sdk',
+  'expect'
+], function load__string_trim_test(exports, dart_sdk, expect) {
+  'use strict';
+  const core = dart_sdk.core;
+  const dart = dart_sdk.dart;
+  const dartx = dart_sdk.dartx;
+  const expect$ = expect.expect;
+  const string_trim_test = Object.create(null);
+  let VoidTodynamic = () => (VoidTodynamic = dart.constFn(dart.definiteFunctionType(dart.dynamic, [])))();
+  string_trim_test.StringTrimTest = class StringTrimTest extends core.Object {
+    static testMain() {
+      expect$.Expect.equals("", " "[dartx.trim]());
+      expect$.Expect.equals("", "     "[dartx.trim]());
+      let a = "      lots of space on the left";
+      expect$.Expect.equals("lots of space on the left", a[dartx.trim]());
+      a = "lots of space on the right           ";
+      expect$.Expect.equals("lots of space on the right", a[dartx.trim]());
+      a = "         lots of space           ";
+      expect$.Expect.equals("lots of space", a[dartx.trim]());
+      a = "  x  ";
+      expect$.Expect.equals("x", a[dartx.trim]());
+      expect$.Expect.equals("", " \t \n \r "[dartx.trim]());
+    }
+  };
+  dart.setSignature(string_trim_test.StringTrimTest, {
+    statics: () => ({testMain: dart.definiteFunctionType(dart.dynamic, [])}),
+    names: ['testMain']
+  });
+  string_trim_test.main = function() {
+    string_trim_test.StringTrimTest.testMain();
+  };
+  dart.fn(string_trim_test.main, VoidTodynamic());
+  // Exports:
+  exports.string_trim_test = string_trim_test;
+});