[Chromecast] Moves persistent UMA client ID handling to common code.

chromecast/browser/metrics/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.
 
 source_set("metrics") {
   sources = [
     "cast_metrics_prefs.cc",
     "cast_metrics_prefs.h",
     "cast_metrics_service_client.cc",
     "cast_metrics_service_client.h",
     "cast_stability_metrics_provider.cc",
     "cast_stability_metrics_provider.h",
-    "platform_metrics_providers.h",
   ]
 
   deps = [
     "//base",
     "//base:i18n",
     "//base:prefs",
     "//chromecast/base",
     "//chromecast/common",
     "//components/metrics",
     "//components/metrics:gpu",
     "//components/metrics:net",
     "//components/metrics:profiler",
     "//content/public/common",
     "//content/public/browser",
   ]
 
   if (is_linux) {
     sources += [
       "external_metrics.cc",
       "external_metrics.h",
     ]
 
     deps += [ "//components/metrics:serialization" ]
   }
-
-  # TODO(kmackay) add source "platform_metrics_providers_simple.cc"
-  #               according to condition (chromecast_branding != "Chrome")
 }