Combine DEBUG_BREAK and DEBUG_PREPARE_STEP_IN into one IC stub kind DEBUG_STUB, encoding DEBUG_BREA…

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 2d8626be72af0bb1123e681adba667e25897eead..1d7ceb06d401b81c858135da9be1dacc3123353f 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -9036,8 +9036,7 @@ const char* Code::ICState2String(InlineCacheState state) {
     case MONOMORPHIC_PROTOTYPE_FAILURE: return "MONOMORPHIC_PROTOTYPE_FAILURE";
     case POLYMORPHIC: return "POLYMORPHIC";
     case MEGAMORPHIC: return "MEGAMORPHIC";
-    case DEBUG_BREAK: return "DEBUG_BREAK";
-    case DEBUG_PREPARE_STEP_IN: return "DEBUG_PREPARE_STEP_IN";
+    case DEBUG_STUB: return "DEBUG_STUB";
   }
   UNREACHABLE();
   return NULL;