kernel->ssa: implement for-in loops

tests/compiler/dart2js/kernel/loops_test.dart

Index: tests/compiler/dart2js/kernel/loops_test.dart
diff --git a/tests/compiler/dart2js/kernel/loops_test.dart b/tests/compiler/dart2js/kernel/loops_test.dart
index 6535e95a3a66a0ddcda2d8c8672bed438c5485a3..a619c360bebf77e7c05da189e1bad412cf13cb46 100644
--- a/tests/compiler/dart2js/kernel/loops_test.dart
+++ b/tests/compiler/dart2js/kernel/loops_test.dart
@@ -7,7 +7,7 @@ import 'package:test/test.dart';
 import 'helper.dart' show check;
 
 main() {
-  test('for-loop', () {
+  test('for loop', () {
     String code = '''
 main() {
   var a = 0;
@@ -19,7 +19,7 @@ main() {
     return check(code);
   });
 
-  test('while-loop', () {
+  test('while loop', () {
     String code = '''
 main() {
   var a = 0;
@@ -30,4 +30,46 @@ main() {
 }''';
     return check(code);
   });
+
+  test('for-in loop', () {
+    String code = '''
+main() {
+  var sum = 0;
+  for (var a in [1, 2, 3]) {
+    sum += a;
+  }
+  return sum;
+}''';
+    // TODO(het): Check that the code is alpha-equivalent. That is,
+    // the same except for variable names.
+    return check(code);
+  }, skip: "The output is the same, with one variable renamed");
+
+  test('for-in loop optimized', () {
+    String code = '''
+main() {
+  var sum = 0;
+  for (var a in [1, 2, 3]) {
+    sum += a;
+  }
+  return sum;
+}''';
+    // This is the same test as above, but by enabling type inference
+    // we allow the compiler to detect that it can iterate over the
+    // array using indexing.
+    return check(code, disableTypeInference: false);
+  });
+
+  test('for-in loop top-level variable', () {
+    String code = '''
+var a = 0;
+main() {
+  var sum = 0;
+  for (a in [1, 2, 3]) {
+    sum += a;
+  }
+  return sum;
+}''';
+    return check(code, disableTypeInference: false);
+  });
 }