Disk cache: fix broken UMA reports.

net/disk_cache/backend_impl.cc

 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/disk_cache/backend_impl.h"
 
 #include "base/file_util.h"
 #include "base/histogram.h"
 #include "base/message_loop.h"
 #include "base/string_util.h"
@@ skipping 1292 matching lines @@
   if (!data_->header.lru.filled)
     return;
 
   // This is an up to date client that will report FirstEviction() data. After
   // that event, start reporting this:
 
   int64 total_hours = stats_.GetCounter(Stats::TIMER) / 120;
   CACHE_UMA(HOURS, "TotalTime", 0, static_cast<int>(total_hours));
 
   int64 use_hours = stats_.GetCounter(Stats::LAST_REPORT_TIMER) / 120;
+  stats_.SetCounter(Stats::LAST_REPORT_TIMER, stats_.GetCounter(Stats::TIMER));
+
+  // We may see users with no use_hours at this point if this is the first time
+  // we are running this code.
+  if (use_hours)
+    use_hours = total_hours - use_hours;
+
   if (!use_hours || !GetEntryCount() || !data_->header.num_bytes)
     return;
 
   CACHE_UMA(HOURS, "UseTime", 0, static_cast<int>(use_hours));
   CACHE_UMA(PERCENTAGE, "HitRatio", 0, stats_.GetHitRatio());
   CACHE_UMA(PERCENTAGE, "ResurrectRatio", 0, stats_.GetResurrectRatio());
 
   int64 trim_rate = stats_.GetCounter(Stats::TRIM_ENTRY) / use_hours;
   CACHE_UMA(COUNTS, "TrimRate", 0, static_cast<int>(trim_rate));
 
   int avg_size = data_->header.num_bytes / GetEntryCount();
   CACHE_UMA(COUNTS, "EntrySize", 0, avg_size);
 
   int large_entries_bytes = stats_.GetLargeEntriesSize();
   int large_ratio = large_entries_bytes * 100 / data_->header.num_bytes;
   CACHE_UMA(PERCENTAGE, "LargeEntriesRatio", 0, large_ratio);
 
   stats_.ResetRatios();
   stats_.SetCounter(Stats::TRIM_ENTRY, 0);
-  stats_.SetCounter(Stats::LAST_REPORT_TIMER, 0);
 }
 
 void BackendImpl::UpgradeTo2_1() {
   // 2.1 is basically the same as 2.0, except that new fields are actually
   // updated by the new eviction algorithm.
   DCHECK(0x20000 == data_->header.version);
   data_->header.version = 0x20001;
   data_->header.lru.sizes[Rankings::NO_USE] = data_->header.num_entries;
 }
 
@@ skipping 105 matching lines @@
 
   return num_dirty;
 }
 
 bool BackendImpl::CheckEntry(EntryImpl* cache_entry) {
   RankingsNode* rankings = cache_entry->rankings()->Data();
   return !rankings->pointer;
 }
 
 }  // namespace disk_cache