Split TemplateHashMapImpl::Lookup into two methods

src/ast-value-factory.cc

Index: src/ast-value-factory.cc
diff --git a/src/ast-value-factory.cc b/src/ast-value-factory.cc
index ff2010007f9bc3f4d33e9c6d5656f04da7bae20c..219be16303129ac70bb2adaae8ae57e56a7a3738 100644
--- a/src/ast-value-factory.cc
+++ b/src/ast-value-factory.cc
@@ -363,7 +363,7 @@ AstRawString* AstValueFactory::GetString(uint32_t hash, bool is_one_byte,
   // against the AstRawStrings which are in the string_table_. We should not
   // return this AstRawString.
   AstRawString key(is_one_byte, literal_bytes, hash);
-  HashMap::Entry* entry = string_table_.Lookup(&key, hash, true);
+  HashMap::Entry* entry = string_table_.LookupOrInsert(&key, hash);
   if (entry->value == NULL) {
     // Copy literal contents for later comparison.
     int length = literal_bytes.length();