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

content/public/browser/content_browser_client.h

Index: content/public/browser/content_browser_client.h
diff --git a/content/public/browser/content_browser_client.h b/content/public/browser/content_browser_client.h
index 2c6734cf1f7c073f8180a46bb76201434db02647..4cd99f3f9006d581bb6eda509ad89f0b05985159 100644
--- a/content/public/browser/content_browser_client.h
+++ b/content/public/browser/content_browser_client.h
@@ -79,6 +79,7 @@ class SelectFilePolicy;
 namespace storage {
 class ExternalMountPoints;
 class FileSystemBackend;
+class QuotaManager;
 }
 
 namespace content {
@@ -425,6 +426,12 @@ class CONTENT_EXPORT ContentBrowserClient {
   // 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