Add support for adding an external and a tagged pointer

src/ppc/lithium-ppc.cc

Index: src/ppc/lithium-ppc.cc
diff --git a/src/ppc/lithium-ppc.cc b/src/ppc/lithium-ppc.cc
index 296f0ac364fce880be25ff33c5e25647eab2b13f..62d1e6682b404a6f4d23347d9cfa08f3ba6d2618 100644
--- a/src/ppc/lithium-ppc.cc
+++ b/src/ppc/lithium-ppc.cc
@@ -1646,7 +1646,10 @@ LInstruction* LChunkBuilder::DoAdd(HAdd* instr) {
     return result;
   } 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));
     LOperand* left = UseRegisterAtStart(instr->left());
     LOperand* right = UseOrConstantAtStart(instr->right());