Reorganize histograms for persistence.

base/metrics/histogram_snapshot_manager.cc

Index: base/metrics/histogram_snapshot_manager.cc
diff --git a/base/metrics/histogram_snapshot_manager.cc b/base/metrics/histogram_snapshot_manager.cc
index a7605aa14179ac6b89a747a201fe0b285eb6dd2d..0b3e9a4550c978c37852a7c2dd5e3539e7f38c14 100644
--- a/base/metrics/histogram_snapshot_manager.cc
+++ b/base/metrics/histogram_snapshot_manager.cc
@@ -42,6 +42,7 @@ void HistogramSnapshotManager::PrepareDelta(const HistogramBase& histogram) {
   // Get up-to-date snapshot of sample stats.
   scoped_ptr<HistogramSamples> snapshot(histogram.SnapshotSamples());
   const std::string& histogram_name = histogram.histogram_name();

[Alexei Svitkine (slow), 2015/12/04 18:21:00]

Inline this into the DLOG(ERROR) since that's the only thing that uses it now.

[bcwhite, 2015/12/04 19:34:46]

Done.

+  const uint64_t histogram_id = histogram.name_hash();

[Alexei Svitkine (slow), 2015/12/04 18:21:00]

Nit: Move this closer to where it's first used - i.e. right above the if
(corruption)

Also, rename to histogram_hash.

[bcwhite, 2015/12/04 19:34:47]

Done.

 
   int corruption = histogram.FindCorruption(*snapshot);
 
@@ -65,23 +66,23 @@ void HistogramSnapshotManager::PrepareDelta(const HistogramBase& histogram) {
     histogram_flattener_->InconsistencyDetected(
         static_cast<HistogramBase::Inconsistency>(corruption));
     // Don't record corrupt data to metrics services.
-    int old_corruption = inconsistencies_[histogram_name];
+    int old_corruption = inconsistencies_[histogram_id];
     if (old_corruption == (corruption | old_corruption))
       return;  // We've already seen this corruption for this histogram.
-    inconsistencies_[histogram_name] |= corruption;
+    inconsistencies_[histogram_id] |= corruption;
     histogram_flattener_->UniqueInconsistencyDetected(
         static_cast<HistogramBase::Inconsistency>(corruption));
     return;
   }
 
   HistogramSamples* to_log;
-  std::map<std::string, HistogramSamples*>::iterator it =
-      logged_samples_.find(histogram_name);
+  std::map<uint64_t, HistogramSamples*>::iterator it =
+      logged_samples_.find(histogram_id);

[Alexei Svitkine (slow), 2015/12/04 18:21:00]

nit: auto it =

[bcwhite, 2015/12/04 19:34:47]

Done.

   if (it == logged_samples_.end()) {
     to_log = snapshot.release();
 
     // This histogram has not been logged before, add a new entry.
-    logged_samples_[histogram_name] = to_log;
+    logged_samples_[histogram_id] = to_log;
   } else {
     HistogramSamples* already_logged = it->second;
     InspectLoggedSamplesInconsistency(*snapshot, already_logged);