mangle: do not mangle reserved class

lib/scope.js

@@ -71,6 +71,9 @@ SymbolDef.prototype = {
                     || this.orig[0] instanceof AST_SymbolDefun))
             || this.orig[0] instanceof AST_SymbolMethod
             || (options.keep_classnames
+                && (this.orig[0] instanceof AST_SymbolClass
+                    || this.orig[0] instanceof AST_SymbolDefClass))
+            || (options.reserved && options.reserved.indexOf(this.name) >= 0
                 && (this.orig[0] instanceof AST_SymbolClass
                     || this.orig[0] instanceof AST_SymbolDefClass));
     },

test/mocha/reserved-class.js

@@ -0,0 +1,27 @@
+var Uglify = require('../../');
+var assert = require("assert");
+
+describe("mangle: reserved_class", function () {
+    var input_js = `
+(function() {
+    class Foo extends HTMLElement {}
+    Foo.reg;
+    class Hello extends HTMLElement {} 
+    Hello.reg;
+})();   
+`;
+    var output_js = '!function(){class e extends HTMLElement{}e.reg;class Hello extends HTMLElement{}Hello.reg}();'
+
+    it("Should test mangle with reserved_class.", function () {
+        var result = Uglify.minify(input_js, {
+            mangle: { 
+                reserved: ['Hello'],
+                properties: false,
+                keep_classnames: false,
+            },
+        });
+        assert.strictEqual(result.code, output_js);
+    });
+
+
+});