Calculate string hash during flattening.

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index 4751165770da93689d0f9fe502d534bb91fde827..34201996b03357bd0c318ff29ccf6a6c44ae96c4 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -2251,6 +2251,16 @@ Object* Heap::LookupSymbol(String* string) {
 }
 
 
+bool Heap::LookupSymbolIfExists(String* string, String** symbol) {
+  if (string->IsSymbol()) {
+    *symbol = string;
+    return true;
+  }
+  SymbolTable* table = SymbolTable::cast(symbol_table_);
+  return table->LookupSymbolIfExists(string, symbol);
+}
+
+
 #ifdef DEBUG
 void Heap::ZapFromSpace() {
   ASSERT(HAS_HEAP_OBJECT_TAG(kFromSpaceZapValue));