[Sync] Initial implementation of foreign sessions suggestions provider.

components/ntp_snippets/content_suggestions_metrics.cc

 // 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.
 
 #include "components/ntp_snippets/content_suggestions_metrics.h"
 
 #include <string>
 #include <type_traits>
 
 #include "base/metrics/histogram.h"
@@ skipping 27 matching lines @@
     "NewTabPage.ContentSuggestions.MenuOpenedScore";
 const char kHistogramVisitDuration[] =
     "NewTabPage.ContentSuggestions.VisitDuration";
 const char kHistogramMoreButtonShown[] =
     "NewTabPage.ContentSuggestions.MoreButtonShown";
 const char kHistogramMoreButtonClicked[] =
     "NewTabPage.ContentSuggestions.MoreButtonClicked";
 
 const char kPerCategoryHistogramFormat[] = "%s.%s";
 
+// Each suffix here should correspond to an entry under histogram suffix
+// ContentSuggestionCategory in histograms.xml.
 std::string GetCategorySuffix(Category category) {
   static_assert(
       std::is_same<decltype(category.id()), typename base::underlying_type<
                                                 KnownCategories>::type>::value,
       "KnownCategories must have the same underlying type as category.id()");
   // Note: Since the underlying type of KnownCategories is int, it's legal to
   // cast from int to KnownCategories, even if the given value isn't listed in
   // the enumeration. The switch still makes sure that all known values are
   // listed here.
   KnownCategories known_category = static_cast<KnownCategories>(category.id());
   switch (known_category) {
     case KnownCategories::RECENT_TABS:
       return "RecentTabs";
     case KnownCategories::DOWNLOADS:
       return "Downloads";
     case KnownCategories::BOOKMARKS:
       return "Bookmarks";
     case KnownCategories::PHYSICAL_WEB_PAGES:
       return "PhysicalWeb";
+    case KnownCategories::FOREIGN_TABS:
+      return "ForeignTabs";
     case KnownCategories::ARTICLES:
       return "Articles";
     case KnownCategories::LOCAL_CATEGORIES_COUNT:
     case KnownCategories::REMOTE_CATEGORIES_OFFSET:
       NOTREACHED();
       break;
   }
   // All other (unknown) categories go into a single "Experimental" bucket.
   return "Experimental";
 }
@@ skipping 159 matching lines @@
 
 void OnMoreButtonClicked(Category category, int position) {
   // The "more" card can appear in addition to the actual suggestions, so add
   // one extra bucket to this histogram.
   LogCategoryHistogramEnumeration(kHistogramMoreButtonClicked, category,
                                   position, kMaxSuggestionsPerCategory + 1);
 }
 
 }  // namespace metrics
 }  // namespace ntp_snippets