Add a SiteEngagementEvictionPolicy.

chrome/browser/engagement/site_engagement_eviction_policy.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 "base/barrier_closure.h"
+#include "chrome/browser/engagement/site_engagement_eviction_policy.h"
+#include "chrome/browser/engagement/site_engagement_service.h"
+#include "content/public/browser/browser_thread.h"
+
+using GetEvictionOriginTask =
+    SiteEngagementEvictionPolicy::GetEvictionOriginTask;
+
+namespace {
+
+const int kExpectedEngagementSites = 200;
+
+}  // namespace
+
+GetEvictionOriginTask::GetEvictionOriginTask(
+    content::BrowserContext* browser_context,
+    const std::map<GURL, int64>& usage_map,
+    int64 global_quota,
+    const storage::GetEvictionOriginCallback& result_callback)
+    : usage_map_(usage_map),
+      global_quota_(global_quota),
+      total_engagement_points_(0),
+      proxy_(browser_context) {
+}
+
+GetEvictionOriginTask::~GetEvictionOriginTask() {
+}
+
+void GetEvictionOriginTask::Start() {
+  DCHECK(per_task_callback_.is_null());
+  per_task_callback_ = base::BarrierClosure(
+      2, base::Bind(&GetEvictionOriginTask::CalculateEvictionOriginAndReply,
+                    base::Unretained(this)));
+
+  std::vector<GURL> origins;
+  for (const auto& usage : usage_map_)
+    origins.push_back(usage.first);
+
+  proxy_.GetScoresForOrigins(
+      origins, base::Bind(&GetEvictionOriginTask::OnDidGetScoresForOrigin,
+                          base::Unretained(this)));
+  proxy_.GetTotalEngagementPoints(
+      base::Bind(&GetEvictionOriginTask::OnDidGetTotalEngagementPoints,
+                 base::Unretained(this)));
+}
+
+void GetEvictionOriginTask::OnDidGetScoresForOrigin(
+    const std::map<GURL, int>& score_map) {
+  score_map_ = score_map;
+  per_task_callback_.Run();
+}
+
+void GetEvictionOriginTask::OnDidGetTotalEngagementPoints(
+    int total_engagement_points) {
+  total_engagement_points_ = total_engagement_points;
+  per_task_callback_.Run();
+}
+
+void GetEvictionOriginTask::CalculateEvictionOriginAndReply() {
+  // This heuristic is intended to optimize for two criteria:
+  // - evict the site that the user cares about least
+  // - evict the least number of sites to get under the quota limit
+  //
+  // The heuristic for deciding the next eviction origin calculates a soft
+  // quota for each origin which is the amount the origin should be allowed to
+  // use based on its engagement and the global quota. The origin that most
+  // exceeds its soft quota is chosen.
+  GURL origin_to_evict;
+  int64 max_overuse = std::numeric_limits<int64>::min();
+  for (const auto& usage : usage_map_) {
+    int64 overuse = usage.second - GetSoftQuotaForOrigin(usage.first);
+    if (overuse > max_overuse) {
+      max_overuse = overuse;
+      origin_to_evict = usage.first;
+    }
+  }
+  result_callback_.Run(origin_to_evict);
+
+  delete this;
+}
+
+int64 GetEvictionOriginTask::GetSoftQuotaForOrigin(const GURL& origin) {
+  double quota_per_point =
+      global_quota_ /
+      std::max(kExpectedEngagementSites * SiteEngagementScore::kMaxPoints,
+               static_cast<double>(total_engagement_points_));
+
+  return score_map_[origin] * quota_per_point;
+}
+
+SiteEngagementEvictionPolicy::SiteEngagementEvictionPolicy(
+    content::BrowserContext* browser_context)
+    : browser_context_(browser_context) {
+}
+
+SiteEngagementEvictionPolicy::~SiteEngagementEvictionPolicy() {
+}
+
+void SiteEngagementEvictionPolicy::GetEvictionOrigin(
+    const std::map<GURL, int64>& usage_map,
+    int64 global_quota,
+    const storage::GetEvictionOriginCallback& callback) {
+  GetEvictionOriginTask* task = new GetEvictionOriginTask(
+      browser_context_, usage_map, global_quota, callback);
+  // The task will delete itself upon completion.
+  task->Start();
+}