Merge array allocation and List._copyFromObjectArray to provide fast path for large arrays.

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index 1fd813208c1a2e417665252cec4919bf1088d390..ac7bf97c21c4e48590aea2afd1ae022a5c50ac2c 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -6242,6 +6242,10 @@ class Array : public Instance {
   // set to an empty array.
   static RawArray* MakeArray(const GrowableObjectArray& growable_array);
 
+  RawArray* Slice(intptr_t start,
+                  intptr_t count,
+                  bool with_type_argument) const;
+
  protected:
   static RawArray* New(intptr_t class_id,
                        intptr_t len,