Rework UMAHistogramHelper and StatisticsDeltaReader into [Chrome]HistogramTester.

chrome/browser/ui/views/passwords/manage_passwords_view_test.cc

Index: chrome/browser/ui/views/passwords/manage_passwords_view_test.cc
diff --git a/chrome/browser/ui/views/passwords/manage_passwords_view_test.cc b/chrome/browser/ui/views/passwords/manage_passwords_view_test.cc
index b1f8f44969adb30cf9ac57f8c97748d582858a58..39d2300a485e0cf2aa57a747481e714f76c33c31 100644
--- a/chrome/browser/ui/views/passwords/manage_passwords_view_test.cc
+++ b/chrome/browser/ui/views/passwords/manage_passwords_view_test.cc
@@ -4,7 +4,7 @@
 
 #include "chrome/browser/ui/views/passwords/manage_passwords_view_test.h"
 
-#include "base/test/statistics_delta_reader.h"
+#include "base/test/histogram_tester.h"

[msw, 2014/07/18 17:30:25]

nit: you don't need to explicitly include this here since it's in the header.

[Mike Lerman, 2014/07/18 18:23:58]

Done.

 #include "chrome/app/chrome_command_ids.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/browser_command_controller.h"
@@ -90,6 +90,6 @@ base::HistogramSamples* ManagePasswordsViewTest::GetSamples(
     const char* histogram) {
   // Ensure that everything has been properly recorded before pulling samples.
   content::RunAllPendingInMessageLoop();
-  return statistics_reader_.GetHistogramSamplesSinceCreation(
-      histogram).release();
+  return histogram_tester_.GetHistogramSamplesSinceCreation(histogram)

[msw, 2014/07/18 17:30:25]

nit: or make this function-local, not a class member, since it's only used here.

[Mike Lerman, 2014/07/18 18:23:58]

The timing of the execution of the constructor is important here, as it gathers
snapshot data as a baseline for comparison. If I remove this from being a class
member, I would instead have to create it in at the beginning of each of the
test methods that calls GetSamples(), and then pass in that HistogramTester to
this object. The current implementation seems cleaner.

+      .release();
 }