Add base::ListValue::Append() overloads for base::Value::{Dict,List}.

Make it a bit simpler to interoperate between the legacy types and the
new types to simplify incremental code migration.

Bug: 1291666
Change-Id: I524022d46e742c5ba5628ad6c3d669ca150b5bc3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3587251
Reviewed-by: Reilly Grant <[email protected]>
Commit-Queue: Daniel Cheng <[email protected]>
Cr-Commit-Position: refs/heads/main@{#992787}
diff --git a/base/values.h b/base/values.h
index f1b25181..64a593e 100644
--- a/base/values.h
+++ b/base/values.h
@@ -1350,6 +1350,11 @@
   using Value::Append;
   // DEPRECATED: prefer `Value::List::Append()`.
   void Append(std::unique_ptr<Value> in_value);
+  // DEPRECATED: prefer `Value::List::Append()`. Provided to simplify
+  // incremental migration and intentionally only defined on ListValue and not
+  // Value.
+  void Append(base::Value::Dict in_dict);
+  void Append(base::Value::List in_list);
 
   // Swaps contents with the `other` list.
   //