Create a synthetic field trial for precache

components/precache/content/precache_manager_unittest.cc

 // Copyright 2013 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/precache/content/precache_manager.h"
 
 #include <stddef.h>
 
 #include <map>
 #include <memory>
@@ skipping 107 matching lines @@
   }
 
   bool was_on_done_called() const {
     return was_on_done_called_;
   }
 
  private:
   bool was_on_done_called_;
 };
 
+void RegisterSyntheticFieldTrial(const base::Time& last_precache_time) {}

[twifkak, 2016/12/08 21:49:22]

Would be nice to add a small check that this is called. e.g. inside
PrecacheManagerUnderTest, add:

MOCK_METHOD1(RegisterSyntheticFieldTrial,
             void(const base::Time& last_precache_time));

and then initialize with that, and add the appropriate EXPECT_CALL to
StartAndFinishPrecaching.

+
 class PrecacheManagerUnderTest : public PrecacheManager {
  public:
   PrecacheManagerUnderTest(content::BrowserContext* browser_context,
                            const syncer::SyncService* const sync_service,
                            const history::HistoryService* const history_service,
                            const base::FilePath& db_path,
                            std::unique_ptr<PrecacheDatabase> precache_database)
       : PrecacheManager(browser_context,
                         sync_service,
                         history_service,
                         db_path,
-                        std::move(precache_database)),
+                        std::move(precache_database),
+                        base::Bind(&precache::RegisterSyntheticFieldTrial)),
         control_group_(false) {}
   bool IsInExperimentGroup() const override { return !control_group_; }
   bool IsInControlGroup() const override { return control_group_; }
   bool IsPrecachingAllowed() const override { return true; }
   void SetInControlGroup(bool in_control_group) {
     control_group_ = in_control_group;
   }
 
  private:
   bool control_group_;
@@ skipping 413 matching lines @@
   expected_histogram_count_map["Precache.Saved"] += 2;
   expected_histogram_count_map["Precache.TimeSinceLastPrecache"] += 2;
   expected_histogram_count_map["Precache.Saved.Freshness"] = 2;
 
   base::RunLoop().RunUntilIdle();
   EXPECT_THAT(histograms_.GetTotalCountsForPrefix("Precache."),
               ContainerEq(expected_histogram_count_map));
 }
 
 }  // namespace precache