Re-reland: Remove register index/code indirection

src/arm/lithium-arm.cc

Index: src/arm/lithium-arm.cc
diff --git a/src/arm/lithium-arm.cc b/src/arm/lithium-arm.cc
index 4ccb02099569aee044ec33830c78530edf620b48..87cbf0996c59ff640356a410bf01b53bd686d255 100644
--- a/src/arm/lithium-arm.cc
+++ b/src/arm/lithium-arm.cc
@@ -444,14 +444,13 @@ LPlatformChunk* LChunkBuilder::Build() {
 
 
 LUnallocated* LChunkBuilder::ToUnallocated(Register reg) {
-  return new(zone()) LUnallocated(LUnallocated::FIXED_REGISTER,
-                                  Register::ToAllocationIndex(reg));
+  return new (zone()) LUnallocated(LUnallocated::FIXED_REGISTER, reg.code());
 }
 
 
 LUnallocated* LChunkBuilder::ToUnallocated(DoubleRegister reg) {
-  return new(zone()) LUnallocated(LUnallocated::FIXED_DOUBLE_REGISTER,
-                                  DoubleRegister::ToAllocationIndex(reg));
+  return new (zone())
+      LUnallocated(LUnallocated::FIXED_DOUBLE_REGISTER, reg.code());
 }