Add DisplayPlacement/Layout mojoms + StructTraits.

ui/display/mojo/display_layout.typemap

Index: ui/display/mojo/display_layout.typemap
diff --git a/ui/display/mojo/display_layout.typemap b/ui/display/mojo/display_layout.typemap
new file mode 100644
index 0000000000000000000000000000000000000000..d524e56201933001c82265460cdc10c14209cd89
--- /dev/null
+++ b/ui/display/mojo/display_layout.typemap
@@ -0,0 +1,20 @@
+# 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 = "//ui/display/mojo/display_layout.mojom"
+public_headers = [ "//ui/display/display_layout.h" ]
+traits_headers = [ "//ui/display/mojo/display_layout_struct_traits.h" ]
+sources = [
+  "//ui/display/mojo/display_layout_struct_traits.cc",
+]
+public_deps = [
+  "//ui/display",
+]
+
+type_mappings = [
+  "display.mojom.Position=display::DisplayPlacement::Position",
+  "display.mojom.OffsetReference=display::DisplayPlacement::OffsetReference",
+  "display.mojom.DisplayPlacement=display::DisplayPlacement",
+  "display.mojom.DisplayLayout=std::unique_ptr<display::DisplayLayout>[move_only]",
+]