Add Smi::Zero and replace all Smi::FromInt(0) calls

src/debug/debug.h

Index: src/debug/debug.h
diff --git a/src/debug/debug.h b/src/debug/debug.h
index c4e8c17246903b90b805fab9c5723e270df72e46..33e4f15c5c13bb22fe6043830637281a6c29bc50 100644
--- a/src/debug/debug.h
+++ b/src/debug/debug.h
@@ -569,11 +569,11 @@ class Debug {
   }
 
   void clear_suspended_generator() {
-    thread_local_.suspended_generator_ = Smi::FromInt(0);
+    thread_local_.suspended_generator_ = Smi::kZero;
   }
 
   bool has_suspended_generator() const {
-    return thread_local_.suspended_generator_ != Smi::FromInt(0);
+    return thread_local_.suspended_generator_ != Smi::kZero;
   }
 
   void OnException(Handle<Object> exception, Handle<Object> promise);