Allow PolicyLoadStatusSample to override reporting method

components/policy/core/common/policy_load_status.h

Index: components/policy/core/common/policy_load_status.h
diff --git a/components/policy/core/common/policy_load_status.h b/components/policy/core/common/policy_load_status.h
index 6c9e907152f44a3a107cca7ab1bf99b3922c8961..82815376b498ee7886d9c02b3d8ba1449f817c2c 100644
--- a/components/policy/core/common/policy_load_status.h
+++ b/components/policy/core/common/policy_load_status.h
@@ -7,13 +7,10 @@
 
 #include <bitset>
 
+#include "base/callback.h"
 #include "base/macros.h"
 #include "components/policy/policy_export.h"
 
-namespace base {
-class HistogramBase;
-}
-
 namespace policy {
 
 // UMA histogram enum for policy load status. Don't change existing constants,
@@ -49,7 +46,14 @@ enum PolicyLoadStatus {
 // for the status codes that were seen on destruction.
 class POLICY_EXPORT PolicyLoadStatusSample {
  public:
-  PolicyLoadStatusSample();
+  using ReportCallback = base::Callback<void(PolicyLoadStatus status)>;
+
+  // If |report_callback| is set, status is sent to this callback. Otherwise,

[emaxx, 2017/05/04 13:00:34]

To me this looks like stretching a single class for two quite different usages.
Also it's a bit worrying to have a generic callback that is being called from
the destructor (it's nontrivial to track down the execution flow; also thinking
about potential reentrancy issues).

Can this be separated into two different classes instead? One just for UMA, as
before, and another would be for your purposes. For instance, if you don't
really need the "automatically call callback on destruction" behavior, then this
can be boiled down to an interface with just Add() and GetAllStatuses().

[ljusten (tachyonic), 2017/05/05 08:16:27]

Thanks, I like that better.

+  // status is sent to a base::LinearHistogram with name |kHistogramName|. Set
+  // the callback in situations where base::LinearHistogram cannot be used, e.g.
+  // when called from Chromium OS code.
+  PolicyLoadStatusSample(
+      const ReportCallback& report_callback = ReportCallback());
   ~PolicyLoadStatusSample();
 
   // Adds a status code.
@@ -57,7 +61,7 @@ class POLICY_EXPORT PolicyLoadStatusSample {
 
  private:
   std::bitset<POLICY_LOAD_STATUS_SIZE> status_bits_;
-  base::HistogramBase* histogram_;
+  ReportCallback report_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(PolicyLoadStatusSample);
 };