IME for Mus: Add ui.mojom.CompositionText and its struct traits.

services/ui/public/interfaces/ime/BUILD.gn

+# Copyright 2016 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("ime") {
+  sources = [
+    "ime.mojom",
+  ]
+
+  public_deps = [
+    "//ui/events/mojo:interfaces",
+    "//ui/gfx/geometry/mojo",
+    "//ui/gfx/range/mojo",
+  ]
+}
+
+mojom("test_interfaces") {
+  sources = [
+    "ime_struct_traits_test.mojom",
+  ]
+
+  public_deps = [
+    ":ime",
+  ]
+}