Add a StatisticsDeltaReader class and use cases

chrome/browser/ui/cocoa/browser/password_generation_bubble_controller_unittest.mm

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "chrome/browser/ui/cocoa/browser/password_generation_bubble_controller.h"
 
 #include "base/logging.h"
-#include "base/metrics/histogram.h"
 #include "base/metrics/histogram_samples.h"
 #include "base/metrics/statistics_recorder.h"
 #include "base/strings/sys_string_conversions.h"
+#include "base/test/statistics_delta_reader.h"
 #include "chrome/browser/ui/cocoa/cocoa_profile_test.h"
 #include "components/autofill/core/browser/password_generator.h"
 #include "components/autofill/core/common/password_form.h"
 #include "testing/gtest_mac.h"
 
-using base::HistogramBase;
-using base::HistogramSamples;
-using base::StatisticsRecorder;
-
 const char kHistogramName[] = "PasswordGeneration.UserActions";
 
 class PasswordGenerationBubbleControllerTest : public CocoaProfileTest {
  public:
   PasswordGenerationBubbleControllerTest()
       : controller_(nil) {}
 
   static void SetUpTestCase() {
-    StatisticsRecorder::Initialize();
+    base::StatisticsRecorder::Initialize();
   }
 
   virtual void SetUp() {
     CocoaProfileTest::SetUp();
 
     generator_.reset(new autofill::PasswordGenerator(20));
 
-    HistogramBase* histogram =
-        StatisticsRecorder::FindHistogram(kHistogramName);
-    if (histogram)
-      original_ = histogram->SnapshotSamples();
-
     SetUpController();
   }
 
   PasswordGenerationBubbleController* controller() { return controller_; }
 
   void SetUpController() {
     autofill::PasswordForm form;
     NSRect frame = [test_window() frame];
     NSPoint point = NSMakePoint(NSMidX(frame), NSMidY(frame));
 
     // |controller_| is self deleting.
     controller_ = [[PasswordGenerationBubbleController alloc]
                     initWithWindow:test_window()
                         anchoredAt:point
                     renderViewHost:nil
                    passwordManager:nil
                     usingGenerator:generator_.get()
                            forForm:form];
   }
 
   void CloseController() {
     [controller_ close];
     [controller_ windowWillClose:nil];
     controller_ = nil;
   }
 
-  HistogramSamples* GetHistogramSamples() {
-    HistogramBase* histogram =
-        StatisticsRecorder::FindHistogram(kHistogramName);
-    if (histogram) {
-      current_ = histogram->SnapshotSamples();
-      if (original_.get())
-        current_->Subtract(*original_.get());
-    }
-    return current_.get();
-  }
-
  protected:
   // Weak.
   PasswordGenerationBubbleController* controller_;
 
-  // Used to determine the histogram changes made just for this specific
-  // test run.
-  scoped_ptr<HistogramSamples> original_;
-
-  scoped_ptr<HistogramSamples> current_;
-
   scoped_ptr<autofill::PasswordGenerator> generator_;
 };
 
 TEST_F(PasswordGenerationBubbleControllerTest, Regenerate) {
   [controller() showWindow:nil];
 
   PasswordGenerationTextField* textfield = controller().textField;
   // Grab the starting password value.
   NSString* before = [textfield stringValue];
 
   // Click on the regenerate icon.
   [textfield simulateIconClick];
 
   // Make sure that the password has changed. Technically this will fail
   // about once every 1e28 times, but not something we really need to worry
   // about.
   NSString* after = [textfield stringValue];
   EXPECT_FALSE([before isEqualToString:after]);
 }
 
 TEST_F(PasswordGenerationBubbleControllerTest, UMALogging) {
+  base::StatisticsDeltaReader statistics_delta_reader;
   [controller() showWindow:nil];
 
   // Do nothing.
   CloseController();
 
-  HistogramSamples* samples = GetHistogramSamples();
+  scoped_ptr<base::HistogramSamples> samples(
+      statistics_delta_reader.GetHistogramSamplesSinceCreation(kHistogramName));
   EXPECT_EQ(
       1,
       samples->GetCount(autofill::password_generation::IGNORE_FEATURE));
   EXPECT_EQ(
       0,
       samples->GetCount(autofill::password_generation::ACCEPT_AFTER_EDITING));
   EXPECT_EQ(
       0,
       samples->GetCount(
           autofill::password_generation::ACCEPT_ORIGINAL_PASSWORD));
 
   SetUpController();
 
   // Pretend like the user changed the password and accepted it.
   [controller() controlTextDidChange:nil];
   [controller() fillPassword:nil];
   CloseController();
 
-  samples = GetHistogramSamples();
+  samples =
+      statistics_delta_reader.GetHistogramSamplesSinceCreation(kHistogramName);
   EXPECT_EQ(
       1,
       samples->GetCount(autofill::password_generation::IGNORE_FEATURE));
   EXPECT_EQ(
       1,
       samples->GetCount(autofill::password_generation::ACCEPT_AFTER_EDITING));
   EXPECT_EQ(
       0,
       samples->GetCount(
           autofill::password_generation::ACCEPT_ORIGINAL_PASSWORD));
 
   SetUpController();
 
   // Just accept the password
   [controller() fillPassword:nil];
   CloseController();
 
-  samples = GetHistogramSamples();
+  samples =
+      statistics_delta_reader.GetHistogramSamplesSinceCreation(kHistogramName);
   EXPECT_EQ(
       1,
       samples->GetCount(autofill::password_generation::IGNORE_FEATURE));
   EXPECT_EQ(
       1,
       samples->GetCount(autofill::password_generation::ACCEPT_AFTER_EDITING));
   EXPECT_EQ(
       1,
       samples->GetCount(
           autofill::password_generation::ACCEPT_ORIGINAL_PASSWORD));
-
 }