[hydrogen] optimize switch with string clauses

src/ast.h

Index: src/ast.h
diff --git a/src/ast.h b/src/ast.h
index 3de00ef5d30c00d6d310ec886d3faf749808fddc..2dfc8e8414228f96f50e3b77222b96fbcb13aa14 100644
--- a/src/ast.h
+++ b/src/ast.h
@@ -710,6 +710,7 @@ class CaseClause: public ZoneObject {
   // Type feedback information.
   void RecordTypeFeedback(TypeFeedbackOracle* oracle);
   bool IsSmiCompare() { return compare_type_ == SMI_ONLY; }
+  bool IsSymbolCompare() { return compare_type_ == SYMBOL_ONLY; }
   bool IsObjectCompare() { return compare_type_ == OBJECT_ONLY; }
 
  private:
@@ -717,7 +718,7 @@ class CaseClause: public ZoneObject {
   Label body_target_;
   ZoneList<Statement*>* statements_;
   int position_;
-  enum CompareTypeFeedback { NONE, SMI_ONLY, OBJECT_ONLY };
+  enum CompareTypeFeedback { NONE, SMI_ONLY, SYMBOL_ONLY, OBJECT_ONLY };
   CompareTypeFeedback compare_type_;
   int compare_id_;
   int entry_id_;