fix corner case in merge_vars (#5353)

fixes #5352

lib/compress.js

@@ -6029,7 +6029,7 @@ Compressor.prototype.compress = function(node) {
             if (node instanceof AST_Call) {
                 var exp = node.expression;
                 var tail = exp.tail_node();
-                if (!is_lambda(tail)) {
+                if (!(tail instanceof AST_LambdaExpression)) {
                     descend();
                     return mark_expression(exp);
                 }
@@ -6042,6 +6042,23 @@ Compressor.prototype.compress = function(node) {
                 tail.walk(tw);
                 return true;
             }
+            if (node instanceof AST_Class) {
+                if (node.name) node.name.walk(tw);
+                if (node.extends) node.extends.walk(tw);
+                node.properties.filter(function(prop) {
+                    if (prop.key instanceof AST_Node) prop.key.walk(tw);
+                    return prop.value;
+                }).forEach(function(prop) {
+                    if (prop.static) {
+                        prop.value.walk(tw);
+                    } else {
+                        push(tw);
+                        prop.value.walk(tw);
+                        pop(tw);
+                    }
+                });
+                return true;
+            }
             if (node instanceof AST_Conditional) {
                 walk_cond(node.condition, node.consequent, node.alternative);
                 return true;