Add a SiteEngagementEvictionPolicy.

chrome/browser/engagement/site_engagement_eviction_policy_unittest.cc

+// Copyright 2015 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/browser/engagement/site_engagement_eviction_policy.h"
+#include "chrome/browser/engagement/site_engagement_service.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace {
+const int64 kGlobalQuota = 25 * 1024;
+}
+
+class TestSiteEngagementEvictionPolicy : public SiteEngagementEvictionPolicy {
+ public:
+  TestSiteEngagementEvictionPolicy() : SiteEngagementEvictionPolicy(nullptr) {}
+
+  ~TestSiteEngagementEvictionPolicy() override {}
+
+  void SetScore(const GURL& origin, int score) {
+    engagment_score_map_[origin] = score;
+  }
+
+ protected:
+  // Overridden in tests.
+  int GetScore(const GURL& origin) override {
+    return engagment_score_map_[origin];
+  }
+
+  int GetTotalEngagementPoints() override {
+    int total = 0;
+    for (const auto& site : engagment_score_map_)
+      total += site.second;
+
+    return total;
+  }
+
+ private:
+  std::map<GURL, int> engagment_score_map_;
+
+  DISALLOW_COPY_AND_ASSIGN(TestSiteEngagementEvictionPolicy);
+};
+
+using SiteEngagementEvictionPolicyTest = testing::Test;
+
+TEST_F(SiteEngagementEvictionPolicyTest, GetEvictionOrigin) {
+  GURL url1("http://www.google.com");
+  GURL url2("http://www.example.com");
+  GURL url3("http://www.spam.me");
+
+  std::map<GURL, int64> usage;
+  usage[url1] = 10 * 1024;
+  usage[url2] = 10 * 1024;
+  usage[url3] = 10 * 1024;
+
+  TestSiteEngagementEvictionPolicy policy;
+  policy.SetScore(url1, 50);
+  policy.SetScore(url2, 25);
+
+  // When 3 sites have equal usage, evict the site with the least engagement.
+  EXPECT_EQ(url3, policy.GetEvictionOriginOnUIThread(usage, kGlobalQuota));
+
+  usage[url2] = usage[url3] + 10;
+
+  // When a site has more engagement, it may get preference over a site with
+  // less usage.
+  EXPECT_EQ(url3, policy.GetEvictionOriginOnUIThread(usage, kGlobalQuota));
+
+  usage[url2] = 15 * 1024;
+  // But exceeding allocated usage too much will still result in being evicted.
+  EXPECT_EQ(url2, policy.GetEvictionOriginOnUIThread(usage, kGlobalQuota));
+}