Rework UMAHistogramHelper and StatisticsDeltaReader into [Chrome]HistogramTester.

chrome/test/base/chrome_histogram_tester.cc

+// 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.
+
+#include "chrome/test/base/chrome_histogram_tester.h"
+
+#include "base/bind.h"
+#include "base/test/test_timeouts.h"
+#include "chrome/test/base/ui_test_utils.h"
+#include "content/public/browser/histogram_fetcher.h"
+
+ChromeHistogramTester::ChromeHistogramTester() {
+}
+
+ChromeHistogramTester::~ChromeHistogramTester() {
+}
+
+
+void ChromeHistogramTester::FetchTestingSnapshot() {
+

[Ilya Sherman, 2014/07/16 18:44:47]

nit: Spurious newline.

[Mike Lerman, 2014/07/16 19:36:36]

Done.

+  scoped_refptr<content::MessageLoopRunner> runner =
+        new content::MessageLoopRunner;
+
+  content::FetchHistogramsAsynchronously(
+      base::MessageLoop::current(),
+      runner->QuitClosure(),
+      // If this call times out, it means that a child process is not
+      // responding, which is something we should not ignore.  The timeout is
+      // set to be longer than the normal browser test timeout so that it will
+      // be prempted by the normal timeout.
+      TestTimeouts::action_max_timeout() * 2);
+  runner->Run();
+}