Making offline previews freshness configurable

components/previews/core/previews_experiments.cc

Index: components/previews/core/previews_experiments.cc
diff --git a/components/previews/core/previews_experiments.cc b/components/previews/core/previews_experiments.cc
index 97ab3e9a0783b0317bd5adf3c015f5acdd9c0685..fc7922cca8a83bf8b79c8419372e9c5761183a63 100644
--- a/components/previews/core/previews_experiments.cc
+++ b/components/previews/core/previews_experiments.cc
@@ -59,6 +59,11 @@ const char kHostIndifferentBlackListDurationInDays[] =
 const char kSingleOptOutDurationInSeconds[] =
     "single_opt_out_duration_in_seconds";
 
+// The amount of time that an offline page is considered fresh enough to be
+// shown as a preview.
+const char kOfflinePreviewFreshnessDurationInDays[] =
+    "offline_preview_freshness_duration_in_days";
+
 // The string that corresponds to enabled for the variation param experiments.
 const char kExperimentEnabled[] = "true";
 
@@ -153,6 +158,15 @@ base::TimeDelta SingleOptOutDuration() {
   return base::TimeDelta::FromSeconds(duration);
 }
 
+base::TimeDelta OfflinePreviewFreshnessDuration() {
+  std::string param_value = ParamValue(kOfflinePreviewFreshnessDurationInDays);
+  int duration;
+  if (!base::StringToInt(param_value, &duration)) {
+    return base::TimeDelta::FromDays(7);

[jianli, 2016/11/29 22:28:43]

nit: Would it be simpler to say "duration = 7;", which will also make the binary
size a bit less?

[RyanSturm, 2016/11/29 22:43:00]

I will write a follow-up CL to change all of the methods in this file to follow
that pattern. I opened a bug, but I'm not going to add a TODO.

crbug.com/669683

+  }
+  return base::TimeDelta::FromDays(duration);

[tbansal1, 2016/11/29 18:05:38]

nit: Add:
DCHECK_LE(0, duration);

[RyanSturm, 2016/11/29 18:22:19]

Acknowledged. I don't think this is necessary, and we likely could miss this if
we send out bad finch params.

+}
+
 }  // namespace params
 
 bool IsIncludedInClientSidePreviewsExperimentsFieldTrial() {