Support base::Feature entries in chrome://flags.

Since base::Features already support toggling via --enable-features=
and --disable-features= flags, integrate with those.

Changes some if statements on FeatureEntry.type to be switch
statements so that future changes to the enum without updating them
result in compile errors.

BUG=544158

Review URL: https://codereview.chromium.org/1408783002

Cr-Commit-Position: refs/heads/master@{#355419}

base/feature_list.cc

@@ -20,11 +20,6 @@ namespace {
 // have more control over initialization timing. Leaky.
 FeatureList* g_instance = nullptr;
 
-// Splits a comma-separated string containing feature names into a vector.
-std::vector<std::string> SplitFeatureListString(const std::string& input) {
-  return SplitString(input, ",", TRIM_WHITESPACE, SPLIT_WANT_NONEMPTY);
-}
-
 }  // namespace
 
 FeatureList::FeatureList() : initialized_(false) {}
@@ -93,6 +88,12 @@ bool FeatureList::IsEnabled(const Feature& feature) {
   return GetInstance()->IsFeatureEnabled(feature);
 }
 
+// static
+std::vector<std::string> FeatureList::SplitFeatureListString(
+    const std::string& input) {
+  return SplitString(input, ",", TRIM_WHITESPACE, SPLIT_WANT_NONEMPTY);
+}
+
 // static
 FeatureList* FeatureList::GetInstance() {
   return g_instance;

base/feature_list.h

@@ -7,6 +7,7 @@
 
 #include <map>
 #include <string>
+#include <vector>
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
@@ -44,7 +45,7 @@ struct BASE_EXPORT Feature {
 // The basic use case is for any feature that can be toggled (e.g. through
 // command-line or an experiment) to have a defined Feature struct, e.g.:
 //
-//   struct base::Feature kMyGreatFeature {
+//   const base::Feature kMyGreatFeature {
 //     "MyGreatFeature", base::FEATURE_ENABLED_BY_DEFAULT
 //   };
 //
@@ -122,6 +123,10 @@ class BASE_EXPORT FeatureList {
   // struct, which is checked in builds with DCHECKs enabled.
   static bool IsEnabled(const Feature& feature);
 
+  // Splits a comma-separated string containing feature names into a vector.
+  static std::vector<std::string> SplitFeatureListString(
+      const std::string& input);
+
   // Returns the singleton instance of FeatureList. Will return null until an
   // instance is registered via SetInstance().
   static FeatureList* GetInstance();