Enable features API for content shell and webview

base/feature_list.cc

Index: base/feature_list.cc
diff --git a/base/feature_list.cc b/base/feature_list.cc
index 853fc4d84e6df24f8c195b0e59c44aad8bc6e721..15b16c53b7592c9b7f4f30875b847f57b4218b8d 100644
--- a/base/feature_list.cc
+++ b/base/feature_list.cc
@@ -35,7 +35,10 @@ bool IsValidFeatureOrFieldTrialName(const std::string& name) {
 
 }  // namespace
 
-FeatureList::FeatureList() : initialized_(false) {}
+FeatureList::FeatureList()
+  : initialized_(false),
+    initialized_from_command_line_(false) {
+}
 
 FeatureList::~FeatureList() {}
 
@@ -48,6 +51,8 @@ void FeatureList::InitializeFromCommandLine(
   // enabled ones (since RegisterOverride() uses insert()).
   RegisterOverridesFromCommandLine(disable_features, OVERRIDE_DISABLE_FEATURE);
   RegisterOverridesFromCommandLine(enable_features, OVERRIDE_ENABLE_FEATURE);
+
+  initialized_from_command_line_ = true;
 }
 
 bool FeatureList::IsFeatureOverriddenFromCommandLine(
@@ -138,10 +143,20 @@ std::vector<std::string> FeatureList::SplitFeatureListString(
 }
 
 // static
-void FeatureList::InitializeInstance() {
-  if (g_instance)
-    return;
-  SetInstance(make_scoped_ptr(new FeatureList));
+void FeatureList::InitializeInstance(const std::string& enable_features,
+                                     const std::string& disable_features) {
+  if (g_instance) {
+    if (g_instance->initialized_from_command_line_) {

[Alexei Svitkine (slow), 2016/03/30 16:44:32]

Are you sure this bit of logic is necessary?

My understanding is that the other places that create an instance do initialize
it from the command line, so if it exists, this would already be true.

[Alexei Svitkine (slow), 2016/03/30 17:12:25]

We chatted more offline. This check is needed to support flags for content
browser tests - since in that case the instance is initialized by test_suite.cc
which is in base/ and can't use the command flags.

Can you add a comment mentioning base/test/test_suite.cc as an example where
this could be false?

[Changwan Ryu, 2016/03/30 17:53:31]

Added some comment.

+      return;
+    } else {

[Alexei Svitkine (slow), 2016/03/30 17:12:25]

Nit: No need for else if there's a return above.

[Changwan Ryu, 2016/03/30 17:53:31]

Done.

+      delete g_instance;
+      g_instance = nullptr;
+    }
+  }
+
+  scoped_ptr<base::FeatureList> feature_list(new base::FeatureList);
+  feature_list->InitializeFromCommandLine(enable_features, disable_features);
+  base::FeatureList::SetInstance(std::move(feature_list));
 }
 
 // static