Enable features API for content shell and webview

base/feature_list.h

Index: base/feature_list.h
diff --git a/base/feature_list.h b/base/feature_list.h
index cf865a1355abb231d03320cb0fabe5e05149b453..c4d6e83f0f925ff7e46cb72e7d37259e20602189 100644
--- a/base/feature_list.h
+++ b/base/feature_list.h
@@ -145,9 +145,13 @@ class BASE_EXPORT FeatureList {
   static std::vector<std::string> SplitFeatureListString(
       const std::string& input);
 
-  // Initializes and sets a default instance of FeatureList if one has not yet
-  // already been set. No-op otherwise.
-  static void InitializeInstance();
+  // Initializes and sets an instance of FeatureList with feature overrides via
+  // command-line flags |enable_features| and |disable_features| if one has not
+  // already been set from command-line flags. No-op otherwise. See
+  // InitializeFromCommandLine for more details about |enable_features| and
+  // |disable_features| parameters.
+  static void InitializeInstance(const std::string& enable_features,
+                                 const std::string& disable_features);
 
   // Returns the singleton instance of FeatureList. Will return null until an
   // instance is registered via SetInstance().
@@ -235,6 +239,9 @@ class BASE_EXPORT FeatureList {
   // result of FinalizeInitialization().
   bool initialized_;
 
+  // Whether this object has been initialized from command line.
+  bool initialized_from_command_line_;
+
   DISALLOW_COPY_AND_ASSIGN(FeatureList);
 };