Handle string + number in hydrogen.

src/hydrogen.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1221 matching lines @@
                                    HValue* map,
                                    ElementsKind from_kind,
                                    ElementsKind to_kind,
                                    bool is_jsarray);
 
   // Do lookup in the number string cache. If the object is not found
   // in the cache, the false branch of the continuation is taken;
   // otherwise the true branch is taken and the returned value contains
   // the cache value for the object. The returned value must NOT be used
   // on the false branch.
+  enum ToStringMode { ALLOW_SIDE_EFFECTS, CHECK_NUMBER };
   HValue* BuildLookupNumberStringCache(HValue* object,
+                                       ToStringMode mode,
                                        HIfContinuation* continuation);
-  HValue* BuildNumberToString(HValue* number);
+  HValue* BuildNumberToString(HValue* number, ToStringMode mode);
 
   HInstruction* BuildUncheckedMonomorphicElementAccess(
       HValue* checked_object,
       HValue* key,
       HValue* val,
       bool is_js_array,
       ElementsKind elements_kind,
       bool is_store,
       LoadKeyedHoleMode load_mode,
       KeyedAccessStoreMode store_mode);
@@ skipping 1219 matching lines @@
   }
 
  private:
   HGraphBuilder* builder_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_H_