[crankshaft] Add support for %_ToString.

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/accessors.h"
 #include "src/allocation.h"
 #include "src/ast.h"
@@ skipping 2206 matching lines @@
   F(SetValueOf)                        \
   F(IsDate)                            \
   F(DateField)                         \
   F(ThrowNotDateError)                 \
   F(StringCharFromCode)                \
   F(StringCharAt)                      \
   F(OneByteSeqStringSetChar)           \
   F(TwoByteSeqStringSetChar)           \
   F(ObjectEquals)                      \
   F(ToObject)                          \
+  F(ToString)                          \
   F(IsFunction)                        \
   F(IsSpecObject)                      \
   F(MathPow)                           \
   F(IsMinusZero)                       \
   F(HasCachedArrayIndex)               \
   F(GetCachedArrayIndex)               \
   F(FastOneByteArrayJoin)              \
   F(DebugBreakInOptimizedCode)         \
   F(StringCharCodeAt)                  \
   F(StringAdd)                         \
@@ skipping 830 matching lines @@
   }
 
  private:
   HGraphBuilder* builder_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_H_