Add support for single sample metrics.

content/common/BUILD.gn

 # Copyright 2014 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("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//media/media_options.gni")
 import("//mojo/public/tools/bindings/mojom.gni")
 import("//ppapi/features/features.gni")
 import("//sandbox/features.gni")
@@ skipping 556 matching lines @@
   sources = [
     "associated_interfaces.mojom",
     "child_memory_coordinator.mojom",
     "frame.mojom",
     "host_zoom.mojom",
     "image_downloader/image_downloader.mojom",
     "indexed_db/indexed_db.mojom",
     "leveldb_wrapper.mojom",
     "media/media_devices.mojom",
     "memory_coordinator.mojom",
+    "metrics.mojom",
     "native_types.mojom",
     "render_frame_message_filter.mojom",
     "render_message_filter.mojom",
     "render_widget_window_tree_client_factory.mojom",
     "renderer.mojom",
     "service_worker/embedded_worker.mojom",
     "service_worker/service_worker.mojom",
     "service_worker/service_worker_event_dispatcher.mojom",
     "service_worker/service_worker_types.mojom",
     "storage_partition_service.mojom",
@@ skipping 26 matching lines @@
     "//url/mojo:url_mojom_origin",
   ]
 
   overridden_deps = [ "//ipc:mojom" ]
   component_deps = [ "//ipc" ]
 
   export_class_attribute = "CONTENT_EXPORT"
   export_define = "CONTENT_IMPLEMENTATION=1"
   export_header = "content/common/content_export.h"
 }