Create a synthetic field trial for precache.

components/precache/core/precache_database.h

 // 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.
 
 #ifndef COMPONENTS_PRECACHE_CORE_PRECACHE_DATABASE_H_
 #define COMPONENTS_PRECACHE_CORE_PRECACHE_DATABASE_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 49 matching lines @@
   void DeleteExpiredPrecacheHistory(const base::Time& current_time);
 
   // Delete all history entries from the database.
   void ClearHistory();
 
   // Setter and getter for the last precache timestamp.
   void SetLastPrecacheTimestamp(const base::Time& time);
   base::Time GetLastPrecacheTimestamp();
 
   // Report precache-related metrics in response to a URL being fetched, where
-  // the fetch was motivated by precaching.
+  // the fetch was motivated by precaching. This is called from the network
+  // delegate, via precache_util.
   void RecordURLPrefetchMetrics(const net::HttpResponseInfo& info,
                                 const base::TimeDelta& latency);
 
-  // Records the precache of an url |url| for top host |referrer_host|.
+  // Records the precache of an url |url| for top host |referrer_host|. This is
+  // called from PrecacheFetcher.
   void RecordURLPrefetch(const GURL& url,
                          const std::string& referrer_host,
                          const base::Time& fetch_time,
                          bool was_cached,
                          int64_t size);
 
   // Report precache-related metrics in response to a URL being fetched, where
   // the fetch was not motivated by precaching. |is_connection_cellular|
   // indicates whether the current network connection is a cellular network.
+  // This is called from the network delegate, via precache_util.
   void RecordURLNonPrefetch(const GURL& url,
                             const base::TimeDelta& latency,
                             const base::Time& fetch_time,
                             const net::HttpResponseInfo& info,
                             int64_t size,
                             int host_rank,
                             bool is_connection_cellular);
 
   // Returns the referrer host entry for the |referrer_host|.
   PrecacheReferrerHostEntry GetReferrerHost(const std::string& referrer_host);
@@ skipping 23 matching lines @@
 
   // Precache quota.
   void SaveQuota(const PrecacheQuota& quota);
   PrecacheQuota GetQuota();
 
   base::WeakPtr<PrecacheDatabase> GetWeakPtr();
 
  private:
   friend class PrecacheDatabaseTest;
   friend class PrecacheFetcherTest;
+  friend class PrecacheManagerTest;
 
   bool IsDatabaseAccessible() const;
 
   // Flushes any buffered write operations. |buffered_writes_| will be empty
   // after calling this function. To maximize performance, all the buffered
   // writes are run in a single database transaction.
   void Flush();
 
   // Same as Flush(), but also updates the flag |is_flush_posted_| to indicate
   // that a flush is no longer posted.
@@ skipping 53 matching lines @@
 
   // This must be the last member of this class.
   base::WeakPtrFactory<PrecacheDatabase> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(PrecacheDatabase);
 };
 
 }  // namespace precache
 
 #endif  // COMPONENTS_PRECACHE_CORE_PRECACHE_DATABASE_H_