Adding performance tests for HQP that represent importance of optimising HistoryItemsForTerms method

testing/perf/scoped_histogram_result_printer.h

Index: testing/perf/scoped_histogram_result_printer.h
diff --git a/testing/perf/scoped_histogram_result_printer.h b/testing/perf/scoped_histogram_result_printer.h
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+// Copyright (c) 2016 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.
+
+#ifndef TESTING_PERF_SCOPED_HISTOGRAM_RESULT_PRINTER_H_
+#define TESTING_PERF_SCOPED_HISTOGRAM_RESULT_PRINTER_H_
+
+#include <string>
+#include <vector>
+
+#include "base/bind.h"
+#include "base/macros.h"
+
+namespace testing {
+class UnitTest;
+}  // namespace  testing
+
+namespace base {
+class HistogramSamples;
+}  // namespace base
+
+namespace perf_test {
+
+// This header contains helpers to create binary perf tests based on histograms.
+//
+// Example:
+//
+// IN_PROC_BROWSER_TEST_F(ObjectWeTest, ActionWeTake) {
+//   perf_test::ScopedHistogramResultPrinter scoped_printer(
+//     perf_test::TestBasedPerfTestPrinter(::testing::UnitTest::GetInstance(),
+//                                         "units"));
+//   scoped_printer.AddHistogramStrict("ThisHistogramWillDefinitelyBeHere",
+//                                     "it_measures_THIS");
+//   scoped_printer.AddHistogramNice("ThisHistogramMightNotHaveResults",
+//                                     "it_measures_this");
+//   ... do ActionWeTake
+// }
+//
+// On a dashboard this will be: ObjectWeTestActionWeTake perf test with
+// measurements it_measures_THIS and it_measures_this.
+//
+// For more examples see omnibox_performance_browsertest.cc
+
+// Callback to tranform collected results to the desired format.
+using HistogramPrinter =
+    base::Callback<void(const base::HistogramSamples&, const std::string&)>;
+
+// Creates HistogramPrinter, base on your test. Use this by default.
+HistogramPrinter TestBasedPerfTestPrinter(const ::testing::UnitTest* test,
+                                          std::string units);
+
+// This is a helper class for binary performance tests based on histograms.
+class ScopedHistogramResultPrinter {
+ public:
+  explicit ScopedHistogramResultPrinter(HistogramPrinter printer);
+
+  // Adding histograms:
+  //   |name| - histogram name (example: "Omnibox.CharTypedToSuggestLatency").
+  //   |measurement| - parametr passed to HistogramPrinter. In TestBased
+  //                   this would be a string, that is displayed on a dashboard.
+  //                   (example: "CharTypedToSuggestLatency").
+
+  // Use this method for adding histograms, which can not be absent at runtime
+  void AddHistogramStrict(std::string name, std::string measurement);
+
+  // Use this method for adding histograms, which can be absent at runtime
+  void AddHistogramNice(std::string name, std::string measurement);
+
+  ~ScopedHistogramResultPrinter();
+
+ private:
+  class HistogramInfo;
+
+  void AddHistogram(std::string name,
+                    std::string measurement,
+                    const bool is_nice);
+  HistogramPrinter printer_;
+  std::vector<HistogramInfo> histograms_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedHistogramResultPrinter);
+};
+
+}  // namespace perf_test
+
+#endif  // TESTING_PERF_SCOPED_HISTOGRAM_RESULT_PRINTER_H_