Add ObjectPool tag for external labels. Use LoadExternalLabel for native calls...

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index c0b9241577e3d24ef7342da39158bf3b0c12fdb3..95315c421cb3bc5185e2875a79e2061c1d8200dc 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -10964,11 +10964,13 @@ void ObjectPool::PrintJSONImpl(JSONStream* stream, bool ref) const {
         jsarr.AddValue(obj);
         break;
       case ObjectPool::kImmediate:
-        // We might want to distingiush between immediates and addresses
-        // in the future.
         imm = RawValueAt(i);
         jsarr.AddValue64(imm);
         break;
+      case ObjectPool::kExternalLabel:
+        imm = RawValueAt(i);
+        jsarr.AddValueF("0x%" Px, imm);
+        break;
       default:
         UNREACHABLE();
       }
@@ -10984,6 +10986,8 @@ void ObjectPool::DebugPrint() const {
       ISL_Print("  %" Pd ": 0x%" Px " %s (obj)\n", i,
           reinterpret_cast<uword>(ObjectAt(i)),
           Object::Handle(ObjectAt(i)).ToCString());
+    } else if (InfoAt(i) == kExternalLabel) {
+      ISL_Print("  %" Pd ": 0x%" Px " (external label)\n", i, RawValueAt(i));
     } else {
       ISL_Print("  %" Pd ": 0x%" Px " (raw)\n", i, RawValueAt(i));
     }