[ignition] Optimize JSGenerator creation

src/code-stub-assembler.h

Index: src/code-stub-assembler.h
diff --git a/src/code-stub-assembler.h b/src/code-stub-assembler.h
index ba35e2582ef9fc30922ddf2f72196dff2aff51db..4ac123480d2b7f4343c1901ea700ebf032ac35c7 100644
--- a/src/code-stub-assembler.h
+++ b/src/code-stub-assembler.h
@@ -1262,6 +1262,11 @@ class V8_EXPORT_PRIVATE CodeStubAssembler : public compiler::CodeAssembler {
   // Create a new AllocationSite and install it into a feedback vector.
   Node* CreateAllocationSiteInFeedbackVector(Node* feedback_vector, Node* slot);
 
+  // Given a recently allocated object {object}, with map {initial_map},
+  // initialize remaining fields appropriately to comply with slack tracking.
+  void HandleSlackTracking(Node* context, Node* object, Node* initial_map,
+                           int start_offset);
+
   enum class IndexAdvanceMode { kPre, kPost };
 
   typedef std::function<void(Node* index)> FastLoopBody;