[Crankshaft] Don't add an instruction twice for %_StringGetLength.

src/hydrogen.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_HYDROGEN_H_
 #define V8_HYDROGEN_H_
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
@@ skipping 1400 matching lines @@
       HValue* elements,
       HValue* checked_key,
       HValue* val,
       HValue* dependency,
       ElementsKind elements_kind,
       PropertyAccessType access_type,
       LoadKeyedHoleMode load_mode = NEVER_RETURN_HOLE);
 
   HInstruction* AddLoadStringInstanceType(HValue* string);
   HInstruction* AddLoadStringLength(HValue* string);
+  HInstruction* BuildLoadStringLength(HValue* string);
   HStoreNamedField* AddStoreMapConstant(HValue* object, Handle<Map> map) {
     return Add<HStoreNamedField>(object, HObjectAccess::ForMap(),
                                  Add<HConstant>(map));
   }
   HLoadNamedField* AddLoadMap(HValue* object,
                               HValue* dependency = NULL);
   HLoadNamedField* AddLoadElements(HValue* object,
                                    HValue* dependency = NULL);
 
   bool MatchRotateRight(HValue* left,
@@ skipping 1601 matching lines @@
   }
 
  private:
   HGraphBuilder* builder_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_H_