Add a kSimd128 machine type for Turbofan.

src/compiler/simplified-lowering.cc

Index: src/compiler/simplified-lowering.cc
diff --git a/src/compiler/simplified-lowering.cc b/src/compiler/simplified-lowering.cc
index 7b0545f049f552cf3fab905b1074df77a59a678a..9306dea54a2ee228f4e8afbbddbb8a3b5e2c7ba4 100644
--- a/src/compiler/simplified-lowering.cc
+++ b/src/compiler/simplified-lowering.cc
@@ -142,6 +142,7 @@ UseInfo TruncatingUseInfoFromRepresentation(MachineRepresentation rep) {
     return UseInfo::TruncatingWord32();
     case MachineRepresentation::kBit:
       return UseInfo::Bool();
+    case MachineRepresentation::kSimd128:  // Fall through.
     case MachineRepresentation::kNone:
       break;
   }
@@ -199,6 +200,9 @@ bool MachineRepresentationIsSubtype(MachineRepresentation r1,
     case MachineRepresentation::kFloat64:
       return r2 == MachineRepresentation::kFloat64 ||
              r2 == MachineRepresentation::kTagged;
+    case MachineRepresentation::kSimd128:
+      return r2 == MachineRepresentation::kSimd128 ||
+             r2 == MachineRepresentation::kTagged;
     case MachineRepresentation::kTagged:
       return r2 == MachineRepresentation::kTagged;
   }