Refactor histogram_persistence to be a class.

chrome/installer/setup/installer_metrics.cc

Index: chrome/installer/setup/installer_metrics.cc
diff --git a/chrome/installer/setup/installer_metrics.cc b/chrome/installer/setup/installer_metrics.cc
index 8e5f0443e437f7589493be0818c56ef397cf2b17..33d039b8516d4371b329598ded4e65a498eda280 100644
--- a/chrome/installer/setup/installer_metrics.cc
+++ b/chrome/installer/setup/installer_metrics.cc
@@ -8,29 +8,32 @@
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/metrics/histogram_base.h"
-#include "base/metrics/histogram_persistence.h"
+#include "base/metrics/persistent_histogram_allocator.h"
 #include "base/metrics/persistent_memory_allocator.h"
 #include "chrome/installer/util/util_constants.h"
 
 namespace installer {
 
 void BeginPersistentHistogramStorage() {
-  base::SetPersistentHistogramMemoryAllocator(
-      new base::LocalPersistentMemoryAllocator(
-          1 << 20, 0,  // 1 MiB
-          installer::kSetupHistogramAllocatorName));
-  base::GetPersistentHistogramMemoryAllocator()->CreateTrackingHistograms(
-      installer::kSetupHistogramAllocatorName);
+  base::PersistentHistogramAllocator::SetGlobalAllocator(
+      make_scoped_ptr(new base::PersistentHistogramAllocator(
+          make_scoped_ptr(new base::LocalPersistentMemoryAllocator(
+              1 << 20, 0,  // 1 MiB
+              installer::kSetupHistogramAllocatorName)))));
+  base::PersistentHistogramAllocator::GetGlobalAllocator()
+      ->CreateTrackingHistograms(installer::kSetupHistogramAllocatorName);
 }
 
 void EndPersistentHistogramStorage(const base::FilePath& target_path) {
+  base::PersistentHistogramAllocator::GetGlobalAllocator()

[Alexei Svitkine (slow), 2016/03/07 16:40:43]

Nit: Save a pointer to base::PersistentHistogramAllocator::GetGlobalAllocator()
in a local since you call it also right below.

[bcwhite, 2016/03/08 00:24:04]

Done.

Hmmm...  Perhaps it's better to export the data() and used() methods directly
from the histogram-allocator and call those.

[Alexei Svitkine (slow), 2016/03/08 19:58:28]

Exporting them looks good.

+      ->UpdateTrackingHistograms();
+  base::PersistentMemoryAllocator* allocator =
+      base::PersistentHistogramAllocator::GetGlobalAllocator()
+          ->memory_allocator();
+
   // For atomicity, first write to a temporary file and then rename it.
   // The ImportantFileWriter would be good for this except it supports only
   // std::string for its data.
-  base::PersistentMemoryAllocator* allocator =
-      base::GetPersistentHistogramMemoryAllocator();
-  allocator->UpdateTrackingHistograms();
-
   base::FilePath file_path = target_path
       .AppendASCII(allocator->Name())
       .AddExtension(L".pma");