Add support for single sample metrics.

components/metrics/public/interfaces/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("call_stack_mojo_bindings") {
   sources = [
     "call_stack_profile_collector.mojom",
   ]
 
   deps = [
     "//mojo/common:common_custom_types",
   ]
 }
 
 mojom("call_stack_mojo_test_bindings") {
   sources = [
     "call_stack_profile_collector_test.mojom",
   ]
 
   deps = [
     ":call_stack_mojo_bindings",
     "//mojo/common:common_custom_types",
   ]
 }
+
+mojom("single_sample_metrics_mojo_bindings") {
+  sources = [
+    "single_sample_metrics.mojom",
+  ]
+}