Create a synthetic field trial for precache.

components/precache/content/precache_manager_unittest.cc

Index: components/precache/content/precache_manager_unittest.cc
diff --git a/components/precache/content/precache_manager_unittest.cc b/components/precache/content/precache_manager_unittest.cc
index a93a2ca8caab07e55e83696db23b33d688e84c9a..cb166d362d2f8bc5d1d95dc851a735d76958b79d 100644
--- a/components/precache/content/precache_manager_unittest.cc
+++ b/components/precache/content/precache_manager_unittest.cc
@@ -130,6 +130,8 @@ class TestPrecacheCompletionCallback {
   bool was_on_done_called_;
 };
 
+void RegisterSyntheticFieldTrial(const base::Time& last_precache_time) {}

[jamartin, 2016/12/21 23:54:34]

Maybe test that this is eventually called with the right time?

[jamartin, 2016/12/21 23:54:34]

Idem.

[twifkak, 2017/01/05 23:53:14]

Done.

[twifkak, 2017/01/05 23:53:14]

Done.

+
 class PrecacheManagerUnderTest : public PrecacheManager {
  public:
   PrecacheManagerUnderTest(
@@ -145,7 +147,8 @@ class PrecacheManagerUnderTest : public PrecacheManager {
                         history_service,
                         data_reduction_proxy_settings,
                         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_; }