Make field trials activated in the GPU process be reflected in browser.

chrome/common/variations/child_process_field_trial_syncer_unittest.cc

+// Copyright 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.
+
+#include "chrome/common/variations/child_process_field_trial_syncer.h"
+
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "base/base_switches.h"
+#include "base/command_line.h"
+#include "base/message_loop/message_loop.h"
+#include "base/metrics/field_trial.h"
+#include "base/run_loop.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace chrome_variations {
+
+namespace {
+
+// TestFieldTrialObserver to listen to be notified by the child process syncer.
+class TestFieldTrialObserver : public base::FieldTrialList::Observer {
+ public:
+  TestFieldTrialObserver() {}
+  ~TestFieldTrialObserver() override {}
+
+  // base::FieldTrial::Observer:
+  void OnFieldTrialGroupFinalized(const std::string& trial_name,
+                                  const std::string& group_name) override {
+    observed_entries_.push_back(std::make_pair(trial_name, group_name));
+  }
+
+  size_t observed_entries_count() const { return observed_entries_.size(); }
+
+  std::pair<std::string, std::string> get_observed_entry(int i) const {
+    return observed_entries_[i];
+  }
+
+ private:
+  std::vector<std::pair<std::string, std::string>> observed_entries_;
+
+  DISALLOW_COPY_AND_ASSIGN(TestFieldTrialObserver);
+};
+
+// Needed because make_pair("a", "b") doesn't convert to std::string pair.
+std::pair<std::string, std::string> MakeStringPair(const std::string& a,
+                                                   const std::string& b) {
+  return std::make_pair(a, b);
+}
+
+}  // namespace
+
+TEST(ChildProcessFieldTrialSyncerTest, FieldTrialState) {
+  base::MessageLoop message_loop;
+  base::FieldTrialList field_trial_list(nullptr);
+
+  base::FieldTrial* trial1 = base::FieldTrialList::CreateFieldTrial("A", "G1");
+  base::FieldTrial* trial2 = base::FieldTrialList::CreateFieldTrial("B", "G2");
+  base::FieldTrial* trial3 = base::FieldTrialList::CreateFieldTrial("C", "G3");
+  // Activate trial3 before command line is produced.
+  trial1->group();
+
+  std::string states_string;
+  base::FieldTrialList::AllStatesToString(&states_string);
+
+  base::CommandLine::ForCurrentProcess()->AppendSwitchASCII(
+      switches::kForceFieldTrials, states_string);
+  EXPECT_EQ("*A/G1/B/G2/C/G3/", states_string);
+
+  // Active trial 2 before creating the syncer.
+  trial2->group();
+
+  TestFieldTrialObserver observer;
+  ChildProcessFieldTrialSyncer syncer(&observer);
+  syncer.InitFieldTrialObserving(*base::CommandLine::ForCurrentProcess());
+
+  // The observer should be notified of activated entries that were not activate
+  // on the command line. In this case, trial 2. (Trial 1 was already active via
+  // command line and so its state shouldn't be notified.)
+  ASSERT_EQ(1U, observer.observed_entries_count());
+  EXPECT_EQ(MakeStringPair("B", "G2"), observer.get_observed_entry(0));
+
+  // Now, activate trial 3, which should also get reflected.
+  trial3->group();
+  // Notifications from field trial activation actually happen via posted tasks,
+  // so invoke the run loop.
+  base::RunLoop().RunUntilIdle();
+
+  ASSERT_EQ(2U, observer.observed_entries_count());
+  EXPECT_EQ(MakeStringPair("C", "G3"), observer.get_observed_entry(1));
+}
+
+}  // namespace chrome_variations