implement AST validation (#3863)

bin/uglifyjs

@@ -68,6 +68,7 @@ program.option("--self", "Build UglifyJS as a library (implies --wrap UglifyJS)"
 program.option("--source-map [options]", "Enable source map/specify source map options.", parse_js());
 program.option("--timings", "Display operations run time on STDERR.");
 program.option("--toplevel", "Compress and/or mangle variables in toplevel scope.");
+program.option("--validate", "Perform validation during AST manipulations.");
 program.option("--verbose", "Print diagnostic messages.");
 program.option("--warn", "Print warning messages.");
 program.option("--wrap <name>", "Embed everything as a function with “exports” corresponding to “name” globally.");
@@ -91,6 +92,7 @@ if (!program.output && program.sourceMap && program.sourceMap.url != "inline") {
     "mangle",
     "sourceMap",
     "toplevel",
+    "validate",
     "wrap"
 ].forEach(function(name) {
     if (name in program) {