Enable SiteEngagementEvictionPolicy behind --enable-site-eviction-policy flag.

content/public/browser/content_browser_client.h

 // Copyright (c) 2012 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.
 
 #ifndef CONTENT_PUBLIC_BROWSER_CONTENT_BROWSER_CLIENT_H_
 #define CONTENT_PUBLIC_BROWSER_CONTENT_BROWSER_CLIENT_H_
 
 #include <map>
 #include <string>
 #include <utility>
@@ skipping 61 matching lines @@
 class TargetPolicy;
 }
 
 namespace ui {
 class SelectFilePolicy;
 }
 
 namespace storage {
 class ExternalMountPoints;
 class FileSystemBackend;
+class QuotaManager;
 }
 
 namespace content {
 
 enum class PermissionType;
 class AccessTokenStore;
 class BrowserChildProcessHost;
 class BrowserContext;
 class BrowserMainParts;
 class BrowserPluginGuestDelegate;
@@ skipping 326 matching lines @@
       BrowserContext* browser_context,
       const GURL& site,
       bool can_be_default,
       std::string* partition_domain,
       std::string* partition_name,
       bool* in_memory);
 
   // Create and return a new quota permission context.
   virtual QuotaPermissionContext* CreateQuotaPermissionContext();
 
+  // Gives the embedder a chance to register a custom QuotaEvictionPolicy for a
+  // storage type.
+  virtual void AddQuotaEvictionPolicies(content::BrowserContext* context,

[raymes, 2015/09/24 01:55:30]

It's a bit unfortunate that we need to add a new content/ API but I see there's
no alternative given what you were saying about site engagement service not
being a component :(

+                                        storage::QuotaManager* quota_manager) {}
+
+
   // Informs the embedder that a certificate error has occured.  If
   // |overridable| is true and if |strict_enforcement| is false, the user
   // can ignore the error and continue. The embedder can call the callback
   // asynchronously. If |result| is not set to
   // CERTIFICATE_REQUEST_RESULT_TYPE_CONTINUE, the request will be cancelled
   // or denied immediately, and the callback won't be run.
   virtual void AllowCertificateError(int render_process_id,
                                      int render_frame_id,
                                      int cert_error,
                                      const net::SSLInfo& ssl_info,
@@ skipping 267 matching lines @@
   // Allows an embedder to provide its own ExternalVideoSurfaceContainer
   // implementation.  Return nullptr to disable external surface video.
   virtual ExternalVideoSurfaceContainer*
   OverrideCreateExternalVideoSurfaceContainer(WebContents* web_contents);
 #endif
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_CONTENT_BROWSER_CLIENT_H_