ntp_tiles::metrics: Add rappor metrics for impression URLs per icon type.

components/ntp_tiles/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.
 
 if (is_android) {
   import("//build/config/android/rules.gni")
 }
 
 static_library("ntp_tiles") {
   sources = [
@@ skipping 28 matching lines @@
     "//components/suggestions",
   ]
   deps = [
     "//components/data_use_measurement/core",
     "//components/favicon/core",
     "//components/favicon_base",
     "//components/google/core/browser",
     "//components/image_fetcher",
     "//components/pref_registry",
     "//components/prefs",
+    "//components/rappor/public",
     "//components/search_engines",
     "//components/url_formatter",
     "//components/variations",
     "//components/variations/service",
   ]
 
   if (is_android) {
     deps += [ "android:ntp_tiles_jni_headers" ]
   }
 }
@@ skipping 11 matching lines @@
 
   public_deps = [
     "//base",
   ]
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
     "icon_cacher_unittest.cc",
+    "metrics_unittest.cc",
     "most_visited_sites_unittest.cc",
     "popular_sites_unittest.cc",
   ]
 
   deps = [
     ":json_unsafe_parser",
     ":ntp_tiles",
     "//base/test:test_support",
     "//components/favicon/core",
     "//components/favicon_base",
     "//components/image_fetcher",
     "//components/pref_registry:test_support",
+    "//components/rappor:test_support",
     "//net:test_support",
     "//testing/gmock",
     "//testing/gtest",
     "//ui/gfx:test_support",
   ]
 }
 
 if (is_android) {
   java_cpp_enum("ntp_tiles_enums_java") {
     sources = [
       "metrics.h",
       "ntp_tile_source.h",
     ]
   }
 }