Some improvements in register usage in lithium compilation of LoadKeyed/StoreKeyed operations.

src/x64/lithium-codegen-x64.h

Index: src/x64/lithium-codegen-x64.h
diff --git a/src/x64/lithium-codegen-x64.h b/src/x64/lithium-codegen-x64.h
index e068f14b5ad94c833b5b17a3019a00846ada9e14..0f8a62a8ca502282e066e1b101a498cbdc174d8d 100644
--- a/src/x64/lithium-codegen-x64.h
+++ b/src/x64/lithium-codegen-x64.h
@@ -341,6 +341,8 @@ class LCodeGen BASE_EMBEDDED {
   void DoStoreKeyedExternalArray(LStoreKeyed* instr);
   void DoStoreKeyedFixedDoubleArray(LStoreKeyed* instr);
   void DoStoreKeyedFixedArray(LStoreKeyed* instr);
+  template <class T>
+      void PrepareKeyForKeyedOp(T* hydrogen_instr, LOperand* key);
 
   Zone* zone_;
   LPlatformChunk* const chunk_;