Add struct traits for base::Value.

mojo/common/values.typemap

Index: mojo/common/values.typemap
diff --git a/mojo/common/values.typemap b/mojo/common/values.typemap
index 6bda9fa650c425a10cb92583960d0438f105874a..069c277940b2c8e083ee310c994b34d4558b5274 100644
--- a/mojo/common/values.typemap
+++ b/mojo/common/values.typemap
@@ -4,12 +4,22 @@
 
 mojom = "//mojo/common/values.mojom"
 public_headers = [ "//base/values.h" ]
-traits_headers = [ "//ipc/ipc_message_utils.h" ]
+traits_headers = [
+  "//ipc/ipc_message_utils.h",
+  "//mojo/common/values_struct_traits.h",
+]
 public_deps = [
+  "//base",
   "//ipc",
 ]
+sources = [
+  "values_struct_traits.cc",
+  "values_struct_traits.h",
+]
 
 type_mappings = [
-  "mojo.common.mojom.DictionaryValue=base::DictionaryValue",
-  "mojo.common.mojom.ListValue=base::ListValue",
+  "mojo.common.mojom.DictionaryValue=std::unique_ptr<base::DictionaryValue>[move_only,nullable_is_same_type]",
+  "mojo.common.mojom.LegacyListValue=base::ListValue",
+  "mojo.common.mojom.ListValue=std::unique_ptr<base::ListValue>[move_only,nullable_is_same_type]",
+  "mojo.common.mojom.Value=std::unique_ptr<base::Value>[move_only,nullable_is_same_type]",
 ]