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;
+}
+
+GURL DoCalculateEvictionOrigin(
+    const scoped_refptr<storage::SpecialStoragePolicy>& special_storage_policy,
+    SiteEngagementScoreProvider* score_provider,
+    const std::map<GURL, int64>& usage_map,
+    int64 global_quota) {
+  // TODO(calamity): Integrate storage access frequency as an input to this
+  // heuristic.
+
+  // 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 = score_provider->GetTotalEngagementPoints();
+
+  for (const auto& usage : usage_map) {
+    GURL origin = usage.first;
+    if (special_storage_policy &&
+        (special_storage_policy->IsStorageUnlimited(origin) ||
+         special_storage_policy->IsStorageDurable(origin))) {
+      continue;
+    }
+
+    // |overuse| can be negative if the soft quota exceeds the usage.
+    int64 overuse = usage.second - GetSoftQuotaForOrigin(
+                                       origin, score_provider->GetScore(origin),
+                                       total_engagement_points, global_quota);
+    if (overuse > max_overuse) {
+      max_overuse = overuse;
+      origin_to_evict = origin;
+    }
+  }
+  return origin_to_evict;
+}
+
+GURL GetSiteEngagementEvictionOriginOnUIThread(
+    const scoped_refptr<storage::SpecialStoragePolicy>& special_storage_policy,
+    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 DoCalculateEvictionOrigin(special_storage_policy, service, usage_map,
+                                   global_quota);
+}
+
+}  // namespace
+
+SiteEngagementEvictionPolicy::SiteEngagementEvictionPolicy(
+    content::BrowserContext* browser_context)
+    : browser_context_(browser_context) {}
+
+SiteEngagementEvictionPolicy::~SiteEngagementEvictionPolicy() {}
+
+void SiteEngagementEvictionPolicy::GetEvictionOrigin(
+    const scoped_refptr<storage::SpecialStoragePolicy>& special_storage_policy,
+    const std::map<GURL, int64>& usage_map,
+    int64 global_quota,
+    const storage::GetOriginCallback& callback) {
+  content::BrowserThread::PostTaskAndReplyWithResult(
+      content::BrowserThread::UI, FROM_HERE,
+      base::Bind(&GetSiteEngagementEvictionOriginOnUIThread,
+                 special_storage_policy, browser_context_, usage_map,
+                 global_quota),
+      callback);
+}
+
+// static
+GURL SiteEngagementEvictionPolicy::CalculateEvictionOrigin(
+    const scoped_refptr<storage::SpecialStoragePolicy>& special_storage_policy,
+    SiteEngagementScoreProvider* score_provider,
+    const std::map<GURL, int64>& usage_map,
+    int64 global_quota) {
+  return DoCalculateEvictionOrigin(special_storage_policy, score_provider,
+                                   usage_map, global_quota);
+}