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 b35d1c0c3a30401e6dd4af75f8b5c2b0de11333c..7fc0dcb26ae7456476170b164a6dac65d89f5899 100644
--- a/components/precache/content/precache_manager_unittest.cc
+++ b/components/precache/content/precache_manager_unittest.cc
@@ -125,6 +125,8 @@ class TestPrecacheCompletionCallback {
   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,
@@ -136,7 +138,8 @@ class PrecacheManagerUnderTest : public PrecacheManager {
                         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_; }