Updating FeatureList default initialization pattern

base/feature_list_unittest.cc

 // Copyright 2015 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.
 
 #include "base/feature_list.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 #include <utility>
@@ skipping 439 matching lines @@
   FeatureList::InitializeInstance("", kFeatureOnByDefaultName);
   EXPECT_FALSE(FeatureList::IsEnabled(kFeatureOnByDefault));
   EXPECT_FALSE(FeatureList::IsEnabled(kFeatureOffByDefault));
 
   // Do not initialize from commandline if we have already.
   FeatureList::InitializeInstance(kFeatureOffByDefaultName, "");
   EXPECT_FALSE(FeatureList::IsEnabled(kFeatureOnByDefault));
   EXPECT_FALSE(FeatureList::IsEnabled(kFeatureOffByDefault));
 }
 
+TEST_F(FeatureListTest, UninitializedInstance_IsEnabledReturnsFalse) {
+  ClearFeatureListInstance();
+  // This test case simulates the calling pattern found in code which does not
+  // explicitly initialize the features list.
+  // All IsEnabled() calls should return the default value in this scenario.
+  EXPECT_EQ(nullptr, FeatureList::GetInstance());
+  EXPECT_TRUE(FeatureList::IsEnabled(kFeatureOnByDefault));
+  EXPECT_EQ(nullptr, FeatureList::GetInstance());
+  EXPECT_FALSE(FeatureList::IsEnabled(kFeatureOffByDefault));
+}
+
 }  // namespace base