Create a synthetic field trial for precache

components/precache/content/precache_manager.cc

Index: components/precache/content/precache_manager.cc
diff --git a/components/precache/content/precache_manager.cc b/components/precache/content/precache_manager.cc
index 327fa2b6b83ceafdd748f932467358cb30803ee7..b76f94a8d2dbef00652e6ab9f14367bddcc14b85 100644
--- a/components/precache/content/precache_manager.cc
+++ b/components/precache/content/precache_manager.cc
@@ -51,16 +51,25 @@ PrecacheManager::PrecacheManager(
     const syncer::SyncService* const sync_service,
     const history::HistoryService* const history_service,
     const base::FilePath& db_path,
-    std::unique_ptr<PrecacheDatabase> precache_database)
+    std::unique_ptr<PrecacheDatabase> precache_database,
+    const base::Callback<void(const base::Time&)>&
+        register_synthetic_field_trial_callback)
     : browser_context_(browser_context),
       sync_service_(sync_service),
       history_service_(history_service),
-      is_precaching_(false) {
+      is_precaching_(false),
+      register_synthetic_field_trial_callback_(
+          register_synthetic_field_trial_callback) {
   precache_database_ = std::move(precache_database);
   BrowserThread::PostTask(
       BrowserThread::DB, FROM_HERE,
       base::Bind(base::IgnoreResult(&PrecacheDatabase::Init),
                  base::Unretained(precache_database_.get()), db_path));
+  BrowserThread::PostTaskAndReplyWithResult(

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

Good idea, sticking it in the PrecacheManager constructor.

+      BrowserThread::DB, FROM_HERE,
+      base::Bind(&PrecacheDatabase::GetLastPrecacheTimestamp,
+                 base::Unretained(precache_database_.get())),
+      base::Bind(&PrecacheManager::RegisterSyntheticFieldTrial, AsWeakPtr()));
 }
 
 PrecacheManager::~PrecacheManager() {
@@ -71,6 +80,11 @@ PrecacheManager::~PrecacheManager() {
                             precache_database_.release());
 }
 
+void PrecacheManager::RegisterSyntheticFieldTrial(
+    const base::Time& last_precache_time) {
+  register_synthetic_field_trial_callback_.Run(last_precache_time);
+}
+
 bool PrecacheManager::IsInExperimentGroup() const {
   // Verify IsPrecachingAllowed() before calling FieldTrialList::FindFullName().
   // This is because field trials are only assigned when requested. This allows