Add base::UnguessableToken

mojo/common/common_custom_types_struct_traits.h

Index: mojo/common/common_custom_types_struct_traits.h
diff --git a/mojo/common/common_custom_types_struct_traits.h b/mojo/common/common_custom_types_struct_traits.h
index 5244cf7a2a6108280136a03f9a3bc385c49a5cb2..82e5a8a7a9a5b285b8937b9a77279d7e58fd6879 100644
--- a/mojo/common/common_custom_types_struct_traits.h
+++ b/mojo/common/common_custom_types_struct_traits.h
@@ -5,8 +5,10 @@
 #ifndef MOJO_COMMON_COMMON_CUSTOM_TYPES_STRUCT_TRAITS_H_
 #define MOJO_COMMON_COMMON_CUSTOM_TYPES_STRUCT_TRAITS_H_
 
+#include "base/unguessable_token.h"
 #include "base/version.h"
 #include "mojo/common/common_custom_types.mojom-shared.h"
+#include "mojo/common/mojo_common_export.h"
 
 namespace mojo {
 
@@ -23,6 +25,26 @@ struct StructTraits<mojo::common::mojom::VersionDataView, base::Version> {
                    base::Version* out);
 };
 
+// If base::UnguessableToken is no longer 128 bits, the logic below and the
+// mojom::UnguessableToken type should be updated.
+static_assert(sizeof(base::UnguessableToken) == 2 * sizeof(uint64_t),
+              "base::UnguessableToken should be of size 2 * sizeof(uint64_t).");
+
+template <>
+struct StructTraits<mojo::common::mojom::UnguessableTokenDataView,
+                 base::UnguessableToken> {
+  static uint64_t high(const base::UnguessableToken& token) {
+    return token.GetHighForSerialization();
+  }
+
+  static uint64_t low(const base::UnguessableToken& token) {
+    return token.GetLowForSerialization();
+  }
+
+  static bool Read(mojo::common::mojom::UnguessableTokenDataView data,
+                   base::UnguessableToken* out);
+};
+
 template <>
 struct StructTraits<mojo::common::mojom::TimeDeltaDataView, base::TimeDelta> {
   static int64_t microseconds(const base::TimeDelta& delta) {