Support experiment to store persistent metrics in memory-mapped file.

chrome/browser/metrics/chrome_metrics_service_client.cc

Index: chrome/browser/metrics/chrome_metrics_service_client.cc
diff --git a/chrome/browser/metrics/chrome_metrics_service_client.cc b/chrome/browser/metrics/chrome_metrics_service_client.cc
index 8cd66d4db17000b03bc145324e92879ac9c0c5a2..cf3a6f0f01b5f1f7e958b21bd5285978685d754d 100644
--- a/chrome/browser/metrics/chrome_metrics_service_client.cc
+++ b/chrome/browser/metrics/chrome_metrics_service_client.cc
@@ -182,6 +182,22 @@ CreateInstallerFileMetricsProvider(bool metrics_reporting_enabled) {
   return file_metrics_provider;
 }
 
+void CleanUpGlobalPersistentHistogramStorage() {
+  // If there is a global metrics file being updated on disk, mark it to be
+  // deleted when the process exits. A normal shutdown is almost complete
+  // so there is no benefit in keeping a file with no new data to be processed
+  // during the next startup sequence.
+  base::GlobalHistogramAllocator* allocator =
+      base::GlobalHistogramAllocator::Get();
+  if (allocator) {

[Alexei Svitkine (slow), 2016/06/28 15:08:00]

Nit: Use early returns instead.

[bcwhite, 2016/06/29 03:17:03]

Done.

+    const base::FilePath& path = allocator->GetPersistentLocation();
+    if (!path.empty()) {
+      base::File file(path, base::File::FLAG_OPEN | base::File::FLAG_READ |
+                            base::File::FLAG_DELETE_ON_CLOSE);
+    }
+  }
+}
+
 }  // namespace
 
 
@@ -213,6 +229,7 @@ ChromeMetricsServiceClient::ChromeMetricsServiceClient(
 
 ChromeMetricsServiceClient::~ChromeMetricsServiceClient() {
   DCHECK(thread_checker_.CalledOnValidThread());
+  CleanUpGlobalPersistentHistogramStorage();
 }
 
 // static