C++ bindings: separate out serialization source set, have "mojom" targets optionally use serializat…

examples/serialization/BUILD.gn

+# Copyright 2015 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")
+
+group("serialization") {
+  deps = [
+    ":serialization_example",
+  ]
+}
+
+executable("serialization_example") {
+  sources = [
+    "main.cc",
+  ]
+
+  deps = [
+    ":serialization_mojom_data_only",
+
+    # This is needed for ASAN builds.
+    "//build/config/sanitizers:deps",
+
+    # This provides an |Environment| implementation needed for the
+    # |:serialization_mojom_data_only| dep above.
+    "//mojo/public/cpp/environment:logging_only",
+  ]
+}
+
+# This template generates a |serialization_mojom_data_only| target which
+# provides C++ serialization bindings for this mojom without bringing in the
+# mojo system.
+mojom("serialization_mojom") {
+  sources = [
+    "serialization.mojom",
+  ]
+}