Add support for adding an external and a tagged pointer

src/x87/lithium-x87.cc

Index: src/x87/lithium-x87.cc
diff --git a/src/x87/lithium-x87.cc b/src/x87/lithium-x87.cc
index 301f128e11afec06245c512b7456e20297856af7..82c48717b583967e510c4ae7f02324113ff3bc1d 100644
--- a/src/x87/lithium-x87.cc
+++ b/src/x87/lithium-x87.cc
@@ -1640,7 +1640,10 @@ LInstruction* LChunkBuilder::DoAdd(HAdd* instr) {
     return DoArithmeticD(Token::ADD, instr);
   } else if (instr->representation().IsExternal()) {
     DCHECK(instr->left()->representation().IsExternal());
-    DCHECK(instr->right()->representation().IsInteger32());
+    DCHECK((instr->external_add_type() == AddOfExternalAndInt32 &&
+            instr->right()->representation().IsInteger32()) ||
+           (instr->external_add_type() == AddOfExternalAndTagged &&
+            instr->right()->representation().IsTagged()));
     DCHECK(!instr->CheckFlag(HValue::kCanOverflow));
     bool use_lea = LAddI::UseLea(instr);
     LOperand* left = UseRegisterAtStart(instr->left());