ensure ie8 works with mangled properties (#2238)

fixes #2234

test/mocha/let.js

@@ -2,16 +2,17 @@ var Uglify = require('../../');
 var assert = require("assert");
 
 describe("let", function() {
-    it("Should not produce reserved keywords as variable name in mangle", function(done) {
-        this.timeout(10000);
-
+    this.timeout(30000);
+    it("Should not produce reserved keywords as variable name in mangle", function() {
         // Produce a lot of variables in a function and run it through mangle.
         var s = '"dddddeeeeelllllooooottttt"; function foo() {';
         for (var i = 0; i < 18000; i++) {
             s += "var v" + i + "=0;";
         }
         s += '}';
-        var result = Uglify.minify(s, {compress: false});
+        var result = Uglify.minify(s, {
+            compress: false
+        }).code;
 
         // Verify that select keywords and reserved keywords not produced
         [
@@ -19,7 +20,7 @@ describe("let", function() {
             "let",
             "var",
         ].forEach(function(name) {
-            assert.strictEqual(result.code.indexOf("var " + name + "="), -1);
+            assert.strictEqual(result.indexOf("var " + name + "="), -1);
         });
 
         // Verify that the variable names that appeared immediately before
@@ -30,9 +31,27 @@ describe("let", function() {
             "eet", "fet",
             "rar", "oar",
         ].forEach(function(name) {
-            assert.ok(result.code.indexOf("var " + name + "=") >= 0);
+            assert.notStrictEqual(result.indexOf("var " + name + "="), -1);
+        });
+    });
+    it("Should quote mangled properties that are reserved keywords", function() {
+        var s = '"rrrrrnnnnniiiiiaaaaa";';
+        for (var i = 0; i < 18000; i++) {
+            s += "v.b" + i + ";";
+        }
+        var result = Uglify.minify(s, {
+            compress: false,
+            ie8: true,
+            mangle: {
+                properties: true,
+            }
+        }).code;
+        [
+            "in",
+            "var",
+        ].forEach(function(name) {
+            assert.notStrictEqual(result.indexOf(name), -1);
+            assert.notStrictEqual(result.indexOf('v["' + name + '"]'), -1);
         });
-
-        done();
     });
 });