Add runtime tests for for-of initializers that are not simple names

Also enables typechecking in Es6ForOfConverterTest for some tests cases

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=202064469

test/com/google/javascript/jscomp/Es6ForOfConverterTest.java

@@ -194,9 +194,6 @@ public void testForOfOnNonIterable() {
   }
 
   public void testForOfWithQualifiedNameInitializer() {
-    // TODO(b/79532975): handle this case in the type checker and remove disableTypeCheck();
-    disableTypeCheck();
-    disableTypeInfoValidation();
     test(
         "var obj = {a: 0}; for (obj.a of [1,2,3]) { console.log(obj.a); }",
         lines(
@@ -212,9 +209,6 @@ public void testForOfWithQualifiedNameInitializer() {
   }
 
   public void testForOfWithComplexInitializer() {
-    // TODO(b/79532975): handle this case in the type checker and remove disableTypeCheck();
-    disableTypeCheck();
-    disableTypeInfoValidation();
     test(
         "function f() { return {}; } for (f()['x' + 1] of [1,2,3]) {}",
         lines(

test/com/google/javascript/jscomp/runtime_tests/for_of_test.js

@@ -106,3 +106,24 @@ function testForOfArrayNested() {
   assertEquals(13, result[7]);
   assertEquals(14, result[8]);
 }
+
+function testForOfWithGetPropInitializer() {
+  const /** {a: number} */ obj = {a: 3};
+  for (obj.a of [4]) {}
+  assertEquals(4, obj.a);
+}
+
+function testForOfWithGetElemInitializer() {
+  const /** !Object<number, number> */ obj = {};
+
+  const /** !Array<number> */ arr = [5, 6, 7];
+  const /** !Array<number> */ newArr = [];
+  var index = 0;
+  for (obj[index] of arr) {
+    newArr.push(obj[index]);
+    index++;
+  }
+
+  assertArrayEquals(arr, newArr);
+  assertObjectEquals({0: 5, 1: 6, 2: 7}, obj);
+}