[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 b084ba474203b2c06a547324a49a1007a3102e12..3a53151399a19f04d65cc5b0258ebc92a5ebc2e4 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();