Add about flag for offline page experiment

components/offline_pages/offline_page_feature.cc

Index: components/offline_pages/offline_page_feature.cc
diff --git a/components/offline_pages/offline_page_feature.cc b/components/offline_pages/offline_page_feature.cc
index 2d63da71eee2b882d35b7f127efd087d6419731d..8d51f527564137aff2d33e4f89293572ae5c2f54 100644
--- a/components/offline_pages/offline_page_feature.cc
+++ b/components/offline_pages/offline_page_feature.cc
@@ -6,7 +6,9 @@
 
 #include <string>
 
+#include "base/command_line.h"
 #include "base/metrics/field_trial.h"
+#include "components/offline_pages/offline_page_switches.h"
 
 #if defined(OS_ANDROID)
 
@@ -18,6 +20,15 @@ const char kOfflinePagesFieldTrialEnabledGroupName[] = "Enabled";
 }  // namespace
 
 bool IsOfflinePagesEnabled() {
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kEnableOfflinePages)) {
+    return true;
+  }
+  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kDisableOfflinePages)) {
+    return false;
+  }
+
   std::string group_name =
       base::FieldTrialList::FindFullName(kOfflinePagesFieldTrialName);
   return group_name == kOfflinePagesFieldTrialEnabledGroupName;