[page_load_metrics] Add a NavigationThrottle for richer abort metrics

components/page_load_metrics/browser/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.
 
 # GYP version: components/page_load_metrics.gypi:page_load_metrics_browser
 static_library("browser") {
   sources = [
+    "metrics_navigation_throttle.cc",
+    "metrics_navigation_throttle.h",
     "metrics_web_contents_observer.cc",
     "metrics_web_contents_observer.h",
     "page_load_metrics_observer.cc",
     "page_load_metrics_observer.h",
     "page_load_metrics_util.cc",
     "page_load_metrics_util.h",
   ]
   public_deps = [
     "//content/public/browser",
   ]
@@ skipping 18 matching lines @@
     "//base",
     "//base/test:test_support",
     "//components/page_load_metrics/common",
     "//components/rappor:test_support",
     "//content/test:test_support",
     "//net",
     "//testing/gtest",
     "//third_party/WebKit/public:blink_headers",
   ]
 }