syncer: add mojo for StringOrdinal.

After migrating app_list from Chrome to Ash, we'll need to pass
StringOrdinal objects between processes for setting app list item
positions, e.g. AppListModel::SetItemPosition.

This commit creates a mojo struct for StringOrdinal so that
//ash/public/interfaces:interfaces_internal can depend on it.

Bug: 733662
Change-Id: I96bbd81a82a53462aa0eb2cdcf9e327045a70051
Reviewed-on: https://chromium-review.googlesource.com/780696Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Pavel Yatsuk <pavely@chromium.org>
Commit-Queue: Jiaquan He <hejq@google.com>
Cr-Commit-Position: refs/heads/master@{#521386}

components/sync/base/ordinal.h

@@ -14,8 +14,17 @@
 #include "base/json/string_escape.h"
 #include "base/logging.h"
 
+namespace mojo {
+template <typename DataViewType, typename T>
+struct StructTraits;
+}
+
 namespace syncer {
 
+namespace mojom {
+class StringOrdinalDataView;
+}
+
 // An Ordinal<T> is an object that can be used for ordering. The
 // Ordinal<T> class has an unbounded dense strict total order, which
 // mean for any Ordinal<T>s a, b and c:
@@ -151,6 +160,9 @@ class Ordinal {
   static_assert(kRadix == kMaxDigitValue + 1, "incorrect ordinal radix");
 
  private:
+  friend struct mojo::StructTraits<syncer::mojom::StringOrdinalDataView,
+                                   Ordinal<Traits>>;
+
   // Returns true iff the given byte string satisfies the criteria for
   // a valid Ordinal.
   static bool IsValidOrdinalBytes(const std::string& bytes);

components/sync/mojo/BUILD.gn

+# Copyright 2017 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import("//mojo/public/tools/bindings/mojom.gni")
+
+mojom("interfaces") {
+  sources = [
+    "syncer.mojom",
+  ]
+}

components/sync/mojo/DEPS

+include_rules = [
+  "+components/sync",
+]

components/sync/mojo/OWNERS

+per-file *.mojom=set noparent
+per-file *.mojom=file://ipc/SECURITY_OWNERS
+per-file *_struct_traits*.*=set noparent
+per-file *_struct_traits*.*=file://ipc/SECURITY_OWNERS
+per-file *.typemap=set noparent
+per-file *.typemap=file://ipc/SECURITY_OWNERS

components/sync/mojo/syncer.mojom

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+module syncer.mojom;
+
+// A StringOrdinal is an Ordinal with range 'a'-'z' for printability
+// of its internal byte string representation.  (Think of
+// StringOrdinal as being short for PrintableStringOrdinal.)  It
+// should be used for data types that want to maintain one or more
+// orderings for sync nodes.
+struct StringOrdinal {
+  array<uint8> bytes;
+};
+

components/sync/mojo/syncer.typemap

+# Copyright 2017 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+mojom = "//components/sync/mojo/syncer.mojom"
+public_headers = [ "//components/sync/model/string_ordinal.h" ]
+traits_headers = [ "//components/sync/mojo/syncer_struct_traits.h" ]
+type_mappings = [ "syncer.mojom.StringOrdinal=syncer::StringOrdinal" ]

components/sync/mojo/syncer_struct_traits.h

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef COMPONENTS_SYNC_MOJO_SYNCER_STRUCT_TRAITS_H_
+#define COMPONENTS_SYNC_MOJO_SYNCER_STRUCT_TRAITS_H_
+
+#include <string>
+
+#include "components/sync/model/string_ordinal.h"
+#include "components/sync/mojo/syncer.mojom-shared.h"
+
+namespace mojo {
+
+template <>
+struct StructTraits<syncer::mojom::StringOrdinalDataView,
+                    syncer::StringOrdinal> {
+  static base::span<const uint8_t> bytes(const syncer::StringOrdinal& ordinal) {
+    return base::make_span(
+        reinterpret_cast<const uint8_t*>(ordinal.bytes_.data()),
+        ordinal.bytes_.length());
+  }
+
+  static bool Read(syncer::mojom::StringOrdinalDataView data,
+                   syncer::StringOrdinal* out) {
+    mojo::ArrayDataView<uint8_t> bytes;
+    data.GetBytesDataView(&bytes);
+    *out = syncer::StringOrdinal(reinterpret_cast<const char*>(bytes.data()));
+    return true;
+  }
+};
+
+}  // namespace mojo
+
+#endif  // COMPONENTS_SYNC_MOJO_SYNCER_STRUCT_TRAITS_H_

components/sync/mojo/typemaps.gni

+# Copyright 2017 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+typemaps = [ "//components/sync/mojo/syncer.typemap" ]

mojo/public/tools/bindings/chromium_bindings_configuration.gni

@@ -11,6 +11,7 @@ _typemap_imports = [
   "//chrome/typemaps.gni",
   "//components/arc/common/typemaps.gni",
   "//components/metrics/public/cpp/typemaps.gni",
+  "//components/sync/mojo/typemaps.gni",
   "//components/typemaps.gni",
   "//content/common/bluetooth/typemaps.gni",
   "//content/common/indexed_db/typemaps.gni",