Introduce a request throttler for limiting requests in mobile NTP.

components/ntp_snippets/request_counter_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 "components/ntp_snippets/request_counter.h"
+
+#include <memory>
+
+#include "base/strings/stringprintf.h"
+#include "components/ntp_snippets/pref_names.h"
+#include "components/prefs/pref_registry_simple.h"
+#include "components/prefs/testing_pref_service.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace ntp_snippets {
+
+class RequestCounterTest : public testing::Test {
+ public:
+  RequestCounterTest() {
+    RequestCounter::RegisterProfilePrefs(test_prefs_.registry());
+    // Use any arbitrary RequestType for this unittest.
+    counter_.reset(new RequestCounter(
+        &test_prefs_, RequestCounter::RequestType::ARTICLE_CONTENT_FETCHER, 2));

[Marc Treib, 2016/07/20 12:58:27]

I'd make the "2" a constant, so it's clearer what it means.

[jkrcal, 2016/07/20 14:20:17]

Done.

+  }
+
+ protected:
+  TestingPrefServiceSimple test_prefs_;
+  std::unique_ptr<RequestCounter> counter_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(RequestCounterTest);
+};
+
+TEST_F(RequestCounterTest, QuotaExceeded) {
+  EXPECT_TRUE(counter_->DemandQuota());
+  EXPECT_TRUE(counter_->DemandQuota());
+  EXPECT_FALSE(counter_->DemandQuota());
+}
+
+TEST_F(RequestCounterTest, ForcedDoesNotCountInQuota) {
+  EXPECT_TRUE(counter_->DemandQuota());
+  counter_->ReportForcedRequest();
+  EXPECT_TRUE(counter_->DemandQuota());
+}
+
+TEST_F(RequestCounterTest, QuotaIsPerDay) {
+  EXPECT_TRUE(counter_->DemandQuota());
+  EXPECT_TRUE(counter_->DemandQuota());
+
+  // Now fake the counter to believe the count comes from yesterday.

[Marc Treib, 2016/07/20 12:58:27]

nit: You're faking the "day" pref, not the counter.

Generally, it would be much nicer to have a controllable FakeTime class, then we
wouldn't have to muck around with the prefs, but it seems we don't have that in
Chrome?!

[jkrcal, 2016/07/20 14:20:17]

I wanted to have that but did not find anything reasonable. 
This was then a way simpler solution.

[Marc Treib, 2016/07/20 15:13:57]

Hah, found it:
https://cs.chromium.org/chromium/src/base/test/simple_test_clock.h
(I did vaguely remember seeing something like that)
The way to use it would be to have a Clock instance in the RequestCounter class
and use that instead of base::Time. Then tests can set it to a SimpleTestClock
instance and control that.
I'll leave it up to you whether you want to do that :)

[jkrcal, 2016/07/20 15:46:22]

Thanks for the pointer! I would like to move on. Thus, I leave it for a further
CL :)

+  int now_day = (base::Time::Now() - base::Time::UnixEpoch()).InDays();
+  test_prefs_.SetInteger(ntp_snippets::prefs::kSnippetFetcherQuotaDay,
+                         now_day - 1);
+
+  // The quota should get reset as the day has changed.
+  EXPECT_TRUE(counter_->DemandQuota());
+}
+
+}  // namespace ntp_snippets