Add chrome://flag to enable the Stale Previews timestamp

chrome/browser/previews/previews_infobar_delegate.cc

Index: chrome/browser/previews/previews_infobar_delegate.cc
diff --git a/chrome/browser/previews/previews_infobar_delegate.cc b/chrome/browser/previews/previews_infobar_delegate.cc
index 110f20885eda515966c239a227430ac53c795f2d..ec43a5275189bea82969c9002f03e323ff549273 100644
--- a/chrome/browser/previews/previews_infobar_delegate.cc
+++ b/chrome/browser/previews/previews_infobar_delegate.cc
@@ -34,6 +34,11 @@
 
 namespace {
 
+const char kMinStalenessParamName[] = "min_staleness_in_minutes";
+const char kMaxStalenessParamName[] = "max_staleness_in_minutes";
+const int kMinStalenessParamDefaultValue = 2;
+const int kMaxStalenessParamDefaultValue = 1440;
+
 void RecordPreviewsInfoBarAction(
     previews::PreviewsType previews_type,
     PreviewsInfoBarDelegate::PreviewsInfoBarAction action) {
@@ -245,13 +250,13 @@ base::string16 PreviewsInfoBarDelegate::GetTimestampText() const {
   }
 
   int min_staleness_in_minutes = base::GetFieldTrialParamByFeatureAsInt(
-      previews::features::kStalePreviewsTimestamp, "min_staleness_in_minutes",
-      0);
+      previews::features::kStalePreviewsTimestamp, kMinStalenessParamName,
+      kMinStalenessParamDefaultValue);
   int max_staleness_in_minutes = base::GetFieldTrialParamByFeatureAsInt(
-      previews::features::kStalePreviewsTimestamp, "max_staleness_in_minutes",
-      0);
+      previews::features::kStalePreviewsTimestamp, kMaxStalenessParamName,
+      kMaxStalenessParamDefaultValue);
 
-  if (min_staleness_in_minutes == 0 || max_staleness_in_minutes == 0)
+  if (min_staleness_in_minutes <= 0 || max_staleness_in_minutes <= 0)
     return base::string16();
 
   base::Time network_time;