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/browser_process.h"
+#include "chrome/browser/engagement/site_engagement_eviction_policy.h"
+#include "chrome/browser/engagement/site_engagement_service.h"
+#include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/profiles/profile_manager.h"
+#include "content/public/browser/browser_thread.h"
+
+namespace {
+
+const int kExpectedEngagementSites = 200;
+
+// Gets the quota that an origin deserves based on its site engagement.
+int64 GetSoftQuotaForOrigin(const GURL& origin,
+                            int score,
+                            int total_engagement_points,
+                            int64 global_quota) {
+  double quota_per_point =
+      global_quota /
+      std::max(kExpectedEngagementSites * SiteEngagementScore::kMaxPoints,
+               static_cast<double>(total_engagement_points));
+
+  return score * quota_per_point;
+}
+
+void ReplyWithEvictionOrigin(const storage::GetEvictionOriginCallback& callback,
+                             const GURL& origin_to_evict) {
+  callback.Run(origin_to_evict);
+}
+
+}  // namespace
+
+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) {
+  content::BrowserThread::PostTaskAndReplyWithResult(
+      content::BrowserThread::UI, FROM_HERE,
+      base::Bind(
+          &GetSiteEngagementEvictionOriginOnUIThread,
+          browser_context_, usage_map, global_quota),
+      base::Bind(&ReplyWithEvictionOrigin, callback));

[michaeln, 2015/07/23 02:22:32]

would it work to use 'callback' here directly without the intermediary function?

[calamity, 2015/07/28 01:07:59]

Done.

+}
+
+// static
+GURL SiteEngagementEvictionPolicy::GetSiteEngagementEvictionOriginOnUIThread(

[raymes, 2015/07/21 09:22:20]

nit: I think we can make this a standalone function too?

[calamity, 2015/07/22 01:57:38]

It won't be able to see the private static method below =(

+        content::BrowserContext* browser_context,
+        const std::map<GURL, int64>& usage_map,
+        int64 global_quota) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+  Profile* profile = Profile::FromBrowserContext(browser_context);
+  SiteEngagementService* service =
+     g_browser_process->profile_manager()->IsValidProfile(profile) ?
+     SiteEngagementService::Get(profile) : nullptr;
+  if (!service)
+    return GURL();
+
+  return SiteEngagementEvictionPolicy::CalculateEvictionOrigin(
+      service, usage_map, global_quota);
+}
+
+// static
+GURL SiteEngagementEvictionPolicy::CalculateEvictionOrigin(
+    SiteEngagementService* service,
+    const std::map<GURL, int64>& usage_map,
+    int64 global_quota) {
+  // 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();
+  int total_engagement_points = service->GetTotalEngagementPoints();
+
+  for (const auto& usage : usage_map) {
+    // |overuse| can be negative if the soft quota exceeds the usage.
+    int64 overuse =
+        usage.second - GetSoftQuotaForOrigin(usage.first,
+                                             service->GetScore(usage.first),
+                                             total_engagement_points,
+                                             global_quota);
+    if (overuse > max_overuse) {
+      max_overuse = overuse;
+      origin_to_evict = usage.first;
+    }
+  }
+  return origin_to_evict;
+}