[Android] Add enhanced bookmark opt-in flag.

chrome/browser/about_flags.cc

Index: chrome/browser/about_flags.cc
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 1c9c99617985ea76745a5e9bba61febbd67e297f..da184e7e7b7d603ae57cddb3d279dcf52ecda508 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -2013,6 +2013,10 @@ void GetSanitizedEnabledFlags(
 bool SkipConditionalExperiment(const Experiment& experiment) {
   if (experiment.internal_name ==
       std::string("enhanced-bookmarks-experiment")) {
+#if defined(OS_ANDROID)
+      // On Android, user can opt in.
+      return false;
+#else
     CommandLine* command_line = CommandLine::ForCurrentProcess();
     // Dont't skip experiment if it has non default value.
     // It means user selected it.
@@ -2020,7 +2024,9 @@ bool SkipConditionalExperiment(const Experiment& experiment) {
       return false;
 
     return !IsEnhancedBookmarksExperimentEnabled();
+#endif
   }
+
   if ((experiment.internal_name == std::string("manual-enhanced-bookmarks")) ||
       (experiment.internal_name ==
            std::string("manual-enhanced-bookmarks-optout"))) {