Rework UMAHistogramHelper and StatisticsDeltaReader into [Chrome]HistogramTester.

chrome/test/nacl/nacl_browsertest_uma.cc

Index: chrome/test/nacl/nacl_browsertest_uma.cc
diff --git a/chrome/test/nacl/nacl_browsertest_uma.cc b/chrome/test/nacl/nacl_browsertest_uma.cc
index fb7a463f7dd8417966533eb8ffae7596fad7706e..8b941bc02ef87af761321e76fcf030202c02501c 100644
--- a/chrome/test/nacl/nacl_browsertest_uma.cc
+++ b/chrome/test/nacl/nacl_browsertest_uma.cc
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "chrome/test/base/uma_histogram_helper.h"
+#include "chrome/test/base/chrome_histogram_tester.h"
 #include "chrome/test/nacl/nacl_browsertest_util.h"
 #include "components/nacl/browser/nacl_browser.h"
 #include "native_client/src/trusted/service_runtime/nacl_error_code.h"
@@ -11,13 +11,13 @@
 namespace {
 
 NACL_BROWSER_TEST_F(NaClBrowserTest, SuccessfulLoadUMA, {
+  ChromeHistogramTester histograms;
   // Load a NaCl module to generate UMA data.
   RunLoadTest(FILE_PATH_LITERAL("nacl_load_test.html"));
 
   // Make sure histograms from child processes have been accumulated in the
   // browser brocess.
-  UMAHistogramHelper histograms;
-  histograms.Fetch();
+  histograms.FetchTestingSnapshot();
 
   // Did the plugin report success?
   histograms.ExpectUniqueSample("NaCl.LoadStatus.Plugin",
@@ -88,6 +88,7 @@ class NaClBrowserTestVcacheExtension:
 
 IN_PROC_BROWSER_TEST_F(NaClBrowserTestVcacheExtension,
                        ValidationCacheOfMainNexe) {
+  ChromeHistogramTester histograms;
   // Hardcoded extension AppID that corresponds to the hardcoded
   // public key in the manifest.json file. We need to load the extension
   // nexe from the same origin, so we can't just try to load the extension
@@ -99,8 +100,7 @@ IN_PROC_BROWSER_TEST_F(NaClBrowserTestVcacheExtension,
 
   // Make sure histograms from child processes have been accumulated in the
   // browser brocess.
-  UMAHistogramHelper histograms;
-  histograms.Fetch();
+  histograms.FetchTestingSnapshot();
   // Should have received 2 validation queries (one for IRT and one for NEXE),
   // and responded with a miss.
   histograms.ExpectBucketCount("NaCl.ValidationCache.Query",
@@ -113,7 +113,7 @@ IN_PROC_BROWSER_TEST_F(NaClBrowserTestVcacheExtension,
 
   // Load it again to hit the cache.
   RunNaClIntegrationTest(full_url, true);
-  histograms.Fetch();
+  histograms.FetchTestingSnapshot();
   // Should have received 2 more validation queries later (IRT and NEXE),
   // and responded with a hit.
   histograms.ExpectBucketCount("NaCl.ValidationCache.Query",
@@ -127,11 +127,11 @@ IN_PROC_BROWSER_TEST_F(NaClBrowserTestVcacheExtension,
 // Test that validation for the 2 PNaCl translator nexes can be cached.
 IN_PROC_BROWSER_TEST_F(NaClBrowserTestPnacl,
                        ValidationCacheOfTranslatorNexes) {
+  ChromeHistogramTester histograms;
   // Run a load test w/ one pexe cache identity.
   RunLoadTest(FILE_PATH_LITERAL("pnacl_options.html?use_nmf=o_0"));
 
-  UMAHistogramHelper histograms;
-  histograms.Fetch();
+  histograms.FetchTestingSnapshot();
   // Should have received 3 validation queries:
   // - One for IRT for actual application
   // - Two for two translator nexes