Consistently make the bounds check for AccessArgumentsAt explicit.

src/x64/lithium-x64.cc

Index: src/x64/lithium-x64.cc
diff --git a/src/x64/lithium-x64.cc b/src/x64/lithium-x64.cc
index dd3054f2da620dd245db260826510a6d9b69d940..add56762531417ef58dc2996978286db7402811d 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -2167,12 +2167,10 @@ LInstruction* LChunkBuilder::DoArgumentsObject(HArgumentsObject* instr) {
 
 
 LInstruction* LChunkBuilder::DoAccessArgumentsAt(HAccessArgumentsAt* instr) {
-  LOperand* arguments = UseRegister(instr->arguments());
+  LOperand* args = UseRegister(instr->arguments());
   LOperand* length = UseTempRegister(instr->length());
   LOperand* index = Use(instr->index());
-  LAccessArgumentsAt* result =
-      new(zone()) LAccessArgumentsAt(arguments, length, index);
-  return AssignEnvironment(DefineAsRegister(result));
+  return DefineAsRegister(new(zone()) LAccessArgumentsAt(args, length, index));
 }