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..fed22201e9e3648e15ff7472dc55026270633ed8 100644
--- a/mojo/common/common_custom_types_struct_traits.h
+++ b/mojo/common/common_custom_types_struct_traits.h
@@ -5,6 +5,7 @@
 #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"
 
@@ -23,6 +24,40 @@ 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) {
+    DCHECK(token);
+    uint64_t high, low;
+    token.Serialize(&high, &low);
+    return high;
+  }
+
+  static uint64_t low(const base::UnguessableToken& token) {
+    DCHECK(token);
+    uint64_t high, low;
+    token.Serialize(&high, &low);
+    return low;
+  }
+
+  static bool Read(mojo::common::mojom::UnguessableTokenDataView data,
+                   base::UnguessableToken* out) {
+    uint64_t high = data.high();
+    uint64_t low = data.low();
+
+    *out = base::UnguessableToken::Deserialize(high, low);
+
+    // Receiving a zeroed UnguessableToken is a security issue.
+    return !out->is_empty();
+  }
+};
+
 template <>
 struct StructTraits<mojo::common::mojom::TimeDeltaDataView, base::TimeDelta> {
   static int64_t microseconds(const base::TimeDelta& delta) {