Split TemplateHashMapImpl::Lookup into two methods

src/ast.cc

Index: src/ast.cc
diff --git a/src/ast.cc b/src/ast.cc
index 8caf9c2a29ec4cc4b1bf33b3eaacd06ecbf5501a..1d21ae1d2be8cab0ad6bf14aece11eeafad5b0cb 100644
--- a/src/ast.cc
+++ b/src/ast.cc
@@ -271,7 +271,7 @@ void ObjectLiteral::CalculateEmitStore(Zone* zone) {
     // If there is an existing entry do not emit a store unless the previous
     // entry was also an accessor.
     uint32_t hash = literal->Hash();
-    ZoneHashMap::Entry* entry = table.Lookup(literal, hash, true, allocator);
+    ZoneHashMap::Entry* entry = table.LookupOrInsert(literal, hash, allocator);
     if (entry->value != NULL) {
       auto previous_kind =
           static_cast<ObjectLiteral::Property*>(entry->value)->kind();