Migrate more tests to ScopedFeatureList.

base/feature_list.h

Index: base/feature_list.h
diff --git a/base/feature_list.h b/base/feature_list.h
index 698ecd533423e06c85a6748bd7d85ab23a46fb96..80209ba6588464d769d48215d4ffc54f23d6ac3b 100644
--- a/base/feature_list.h
+++ b/base/feature_list.h
@@ -163,6 +163,8 @@ class BASE_EXPORT FeatureList {
 
   // Registers the given |instance| to be the singleton feature list for this
   // process. This should only be called once and |instance| must not be null.
+  // Note: If you are considering using this for the purposes of testing, take
+  // a look at using base/test/scoped_feature_list.h instead.

[Ilya Sherman, 2016/11/08 00:20:00]

Maybe we should remove ClearInstanceForTesting() from the public API, to better
discourage tests from using SetInstance()?  I think we made
ClearInstanceForTesting() public prior to implementing a scoped feature list for
tests.

[Alexei Svitkine (slow), 2016/11/08 08:03:58]

It's still being used from a few places - such as test harness runners and
ScopedFeatureList itself, so we can't remove it for now unless we find
replacements for those.

   static void SetInstance(std::unique_ptr<FeatureList> instance);
 
   // Clears the previously-registered singleton instance for tests and returns