Get rid of the HInstanceSize instruction.

src/x64/lithium-codegen-x64.cc

Index: src/x64/lithium-codegen-x64.cc
diff --git a/src/x64/lithium-codegen-x64.cc b/src/x64/lithium-codegen-x64.cc
index ab192d683daf74329c1377ce7e90afd2982da1c7..5249a345ee890a09abe67781a5a6ec0057bc93f5 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -2537,14 +2537,6 @@ void LCodeGen::DoDeferredInstanceOfKnownGlobal(LInstanceOfKnownGlobal* instr,
 }
 
 
-void LCodeGen::DoInstanceSize(LInstanceSize* instr) {
-  Register object = ToRegister(instr->object());
-  Register result = ToRegister(instr->result());
-  __ movq(result, FieldOperand(object, HeapObject::kMapOffset));
-  __ movzxbq(result, FieldOperand(result, Map::kInstanceSizeOffset));
-}
-
-
 void LCodeGen::DoCmpT(LCmpT* instr) {
   Token::Value op = instr->op();