Add enable-offlining-recent-pages feature switch.

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 ed390b8815e0abe9990d76c5fa0f1bfefbb11ebb..ab00925cf73069a62c29a4fdd30c6057a5374372 100644
--- a/components/offline_pages/offline_page_feature.cc
+++ b/components/offline_pages/offline_page_feature.cc
@@ -7,14 +7,13 @@
 #include <string>
 
 #include "base/command_line.h"
+#include "base/feature_list.h"
 #include "base/metrics/field_trial.h"
 #include "base/strings/string_util.h"
 #include "build/build_config.h"
 #include "components/offline_pages/offline_page_switches.h"
 #include "components/version_info/version_info.h"
 
-#if defined(OS_ANDROID)
-
 namespace offline_pages {
 
 namespace {
@@ -26,6 +25,10 @@ const char kEnabledAsBookmarksGroupName[] = "EnabledAsBookmarks";
 const char kEnabledAsSavedPagesGroupName[] = "EnabledAsSavedPages";
 }  // namespace
 
+const base::Feature kOffliningRecentPagesFeature {
+   "offline-recent-pages", base::FEATURE_DISABLED_BY_DEFAULT
+};
+
 FeatureMode GetOfflinePageFeatureMode() {
   // Note: It's important to query the field trial state first, to ensure that
   // UMA reports the correct group.
@@ -75,6 +78,9 @@ bool IsOfflinePagesEnabled() {
          mode == FeatureMode::ENABLED_AS_SAVED_PAGES;
 }
 
-}  // namespace offline_pages
+bool IsOffliningRecentPagesEnabled() {
+  return  base::FeatureList::IsEnabled(kOffliningRecentPagesFeature) &&

[rkaplow, 2016/03/08 19:39:42]

this is a little bit confusing, because the isOfflinePagesEnabled then checks
the experimentation state.
One of the main points of the feature API is you don't need to manually check
the command line state and the field trial state anymore, the feature API
handles this:
https://code.google.com/p/chromium/codesearch#chromium/src/components/offline...

I guess this is just for offline pages which are recent, versus the full offline
pages experiment which is broader in scope.

SO the recent pages versus is on iff the experiment for offline pages is on
*and* the flag is set?

I'mn also a bit confused how you will be controlling how users are using this
feature - right now there's no experimentation control.

It seems it may make sense to put this as a experiment parameter in the
OfflinePages experiment. Then you can specify for each of your OfflinePages
groups which ones have the param set.

You can still leave the feature API setup you've already done to control the
state via flags - that is, if you really want users to manually opt into the
feature.

Does this overall make sense? Can ping me if you have questions.

+          IsOfflinePagesEnabled();
+}
 
-#endif
+}  // namespace offline_pages