Support saving browser metrics to disk and reading them during next run.

components/metrics/metrics_service.cc

Index: components/metrics/metrics_service.cc
diff --git a/components/metrics/metrics_service.cc b/components/metrics/metrics_service.cc
index 7e31ddb93156bf301ef333bd5cbe71bb7acc9691..e1ed8d0093cc7588af8632c5ed492b9fc18ab419 100644
--- a/components/metrics/metrics_service.cc
+++ b/components/metrics/metrics_service.cc
@@ -1155,11 +1155,23 @@ void MetricsService::RecordCurrentHistograms() {
 
 void MetricsService::RecordCurrentStabilityHistograms() {
   DCHECK(log_manager_.current_log());
+  histogram_snapshot_manager_.StartDeltas();
   // "true" indicates that StatisticsRecorder should include histograms in
   // persistent storage.
-  histogram_snapshot_manager_.PrepareDeltas(
-      base::StatisticsRecorder::begin(true), base::StatisticsRecorder::end(),
-      base::Histogram::kNoFlags, base::Histogram::kUmaStabilityHistogramFlag);
+  for (auto it = base::StatisticsRecorder::begin(true),
+            end = base::StatisticsRecorder::end();
+       it != end; ++it) {
+    // kUmaStabilityHistogramFlag is actually a combination of two flags and
+    // so the result of the bitwise-and must be checked against the "flag"
+    // value or incorrect matches will occur.
+    if (((*it)->flags() & base::Histogram::kUmaStabilityHistogramFlag) ==
+        base::Histogram::kUmaStabilityHistogramFlag) {
+      histogram_snapshot_manager_.PrepareDelta(*it);
+    }
+  }
+  for (MetricsProvider* provider : metrics_providers_)
+    provider->RecordInitialHistogramSnapshots(&histogram_snapshot_manager_);
+  histogram_snapshot_manager_.FinishDeltas();
 }
 
 void MetricsService::LogCleanShutdown() {