Implement ping_freshness for update_client.

components/update_client/persisted_data.cc

Index: components/update_client/persisted_data.cc
diff --git a/components/update_client/persisted_data.cc b/components/update_client/persisted_data.cc
index 0894dba0d0d333108d2ebcd4ef9ceb9b44ed910b..ad3744f5de5f51310c519f9386f06f2ff3db6b01 100644
--- a/components/update_client/persisted_data.cc
+++ b/components/update_client/persisted_data.cc
@@ -7,6 +7,7 @@
 #include <string>
 #include <vector>
 
+#include "base/guid.h"
 #include "base/macros.h"
 #include "base/threading/thread_checker.h"
 #include "base/values.h"
@@ -16,6 +17,7 @@
 
 const char kPersistedDataPreference[] = "updateclientdata";
 const int kDateLastRollCallUnknown = -2;
+const std::string kPingFreshnessUnknown = "";
 
 namespace update_client {
 
@@ -40,6 +42,20 @@ int PersistedData::GetDateLastRollCall(const std::string& id) const {
   return dlrc;
 }
 
+std::string PersistedData::GetPingFreshness(const std::string& id) const {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  if (!pref_service_)
+    return kPingFreshnessUnknown;
+  std::string freshness = kPingFreshnessUnknown;

[Sorin Jianu, 2016/04/15 20:26:53]

Is there a need to define kPingFreshnessUnknown at all? We could just return
std::string().

[waffles, 2016/04/15 21:54:20]

Done.

+  const base::DictionaryValue* dict =
+      pref_service_->GetDictionary(kPersistedDataPreference);
+  // We assume ids do not contain '.' characters.
+  DCHECK_EQ(std::string::npos, id.find('.'));
+  if (!dict->GetString("apps." + id + ".pf", &freshness))
+    return kPingFreshnessUnknown;
+  return "{" + freshness + "}";

[Sorin Jianu, 2016/04/15 20:26:53]

if we need to format I suggest stringprintf, since expressions like this may
result in temporary variables being created.

This pattern is uses in other places in this CL and previous CLs. It might be
worth reviewing its usage.

I have to do some science with C++11 and the current compilers, since I believe
in some cases, it may avoid creating some of the temporaries. I am not concerned
about time efficiency but it space efficiency due to additional code needed to
create and destroy the temporaries.

[waffles, 2016/04/15 21:54:20]

Done.

+}
+
 void PersistedData::SetDateLastRollCall(const std::vector<std::string>& ids,
                                         int datenum) const {
   DCHECK(thread_checker_.CalledOnValidThread());
@@ -50,6 +66,7 @@ void PersistedData::SetDateLastRollCall(const std::vector<std::string>& ids,
     // We assume ids do not contain '.' characters.
     DCHECK_EQ(std::string::npos, id.find('.'));
     update->SetInteger("apps." + id + ".dlrc", datenum);
+    update->SetString("apps." + id + ".pf", base::GenerateGUID());
   }
 }