Introduce HObjectAccess, which is used by LoadNamedField and StoreNamedField to denote what parts

src/mips/lithium-mips.cc

Index: src/mips/lithium-mips.cc
diff --git a/src/mips/lithium-mips.cc b/src/mips/lithium-mips.cc
index 4b7294470d84cf08d31624c30c5e478f0f78528a..a33e9e609e6b6b9a2c57943db01d0adf9de46f21 100644
--- a/src/mips/lithium-mips.cc
+++ b/src/mips/lithium-mips.cc
@@ -378,8 +378,7 @@ void LAccessArgumentsAt::PrintDataTo(StringStream* stream) {
 
 void LStoreNamedField::PrintDataTo(StringStream* stream) {
   object()->PrintTo(stream);
-  stream->Add(".");
-  stream->Add(*String::cast(*name())->ToCString());
+  stream->Add(".@%d", offset());  // TODO(titzer): use HObjectAccess
   stream->Add(" <- ");
   value()->PrintTo(stream);
 }