Add histograms to track age of cache entries for web fonts

net/disk_cache/blockfile/webfonts_histogram.cc

Index: net/disk_cache/blockfile/webfonts_histogram.cc
diff --git a/net/disk_cache/blockfile/webfonts_histogram.cc b/net/disk_cache/blockfile/webfonts_histogram.cc
index ad157176cd8250b58963a2d85c91aff73c9eddc7..d24df362763fe174449212b67ec2769fed7ef846 100644
--- a/net/disk_cache/blockfile/webfonts_histogram.cc
+++ b/net/disk_cache/blockfile/webfonts_histogram.cc
@@ -78,21 +78,27 @@ void RecordEvictedEntry(const std::string& key) {
 }
 
 void RecordCacheHit(EntryImpl* entry) {
-  const char* label = HistogramLabel(entry->entry()->Data()->key);
+  EntryStore* info = entry->entry()->Data();
+  const char* label = HistogramLabel(info->key);

[rvargas (doing something else), 2014/06/10 23:15:33]

I just realized that this is wrong. This should not be accessing the key field
directly, it should be calling entry->GetKey()

[Kunihiko Sakamoto, 2014/06/11 01:50:10]

Done.

   if (!label)
     return;
   CACHE_HISTOGRAM_COUNTS_10000(HistogramName("DiskCache.ReuseCount.Hit", label),
-                               entry->entry()->Data()->reuse_count);
+                               info->reuse_count);
+  CACHE_HISTOGRAM_AGE(HistogramName("DiskCache.EntryAge.Hit", label),
+                      base::Time::FromInternalValue(info->creation_time));
   RecordCacheEvent(CACHE_EVENT_HIT, label);
 }
 
 void RecordEviction(EntryImpl* entry) {
-  const char* label = HistogramLabel(entry->entry()->Data()->key);
-  if (label)
+  EntryStore* info = entry->entry()->Data();
+  const char* label = HistogramLabel(info->key);
+  if (!label)
     return;
   CACHE_HISTOGRAM_COUNTS_10000(
       HistogramName("DiskCache.ReuseCount.Evict", label),
-      entry->entry()->Data()->reuse_count);
+      info->reuse_count);
+  CACHE_HISTOGRAM_AGE(HistogramName("DiskCache.EntryAge.Evict", label),
+                      base::Time::FromInternalValue(info->creation_time));
 }
 
 }  // namespace web_fonts_histogram