Adds mojom structure for ui::Accelerator and struct traits

ui/base/accelerators/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 = [
+    "accelerator.mojom",
+  ]
+  public_deps = [
+    "//ui/events/mojo:interfaces",
+  ]
+}
+
+source_set("struct_traits") {
+  sources = [
+    "accelerator_struct_traits.h",
+  ]
+  public_deps = [
+    ":interfaces",
+    "//ui/base",
+    "//ui/events",
+  ]
+}
+
+source_set("unittests") {
+  testonly = true
+  sources = [
+    "accelerator_struct_traits_unittest.cc",
+  ]
+  deps = [

[msw, 2017/03/16 22:50:39]

optional nit: you might be able to omit the public_deps of ":struct_traits"?

[sky, 2017/03/16 23:30:46]

The reason to make the deps public_deps is that the header includes all those
files, which means anyone including the header needs to include them as well.

+    ":interfaces",
+    ":struct_traits",
+    "//testing/gtest",
+    "//ui/base",
+    "//ui/events",
+  ]
+}