[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 2a631f2fd69df048f1230cd81bc90320d9cca931..fb9f451c6424cbefb3c131e755564fddb3ba4f73 100644
--- a/src/code-stub-assembler.h
+++ b/src/code-stub-assembler.h
@@ -1267,6 +1267,11 @@ 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;