[destructuring] Parse binding patterns in formal parameters.

src/preparser.cc

Index: src/preparser.cc
diff --git a/src/preparser.cc b/src/preparser.cc
index ddea1792781a5d10310b2095b9c67e7dff9531f2..c6bde4425b92df9153d63f802c286c8a08148271 100644
--- a/src/preparser.cc
+++ b/src/preparser.cc
@@ -549,7 +549,7 @@ PreParser::Statement PreParser::ParseVariableDeclarations(
           ParsePrimaryExpression(&pattern_classifier, CHECK_OK);
       ValidateBindingPattern(&pattern_classifier, CHECK_OK);
 
-      if (!FLAG_harmony_destructuring && !pattern.IsIdentifier()) {
+      if (!allow_harmony_destructuring() && !pattern.IsIdentifier()) {
         ReportUnexpectedToken(next);
         *ok = false;
         return Statement::Default();