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

chrome/browser/chrome_content_browser_client.cc

Index: chrome/browser/chrome_content_browser_client.cc
diff --git a/chrome/browser/chrome_content_browser_client.cc b/chrome/browser/chrome_content_browser_client.cc
index 62fa372215ae9470f7480e6e8e28188cdf94091d..6a3b9bb3c8812a9d321c7230ec21fde6621ab847 100644
--- a/chrome/browser/chrome_content_browser_client.cc
+++ b/chrome/browser/chrome_content_browser_client.cc
@@ -41,6 +41,7 @@
 #include "chrome/browser/defaults.h"
 #include "chrome/browser/devtools/chrome_devtools_manager_delegate.h"
 #include "chrome/browser/download/download_prefs.h"
+#include "chrome/browser/engagement/site_engagement_eviction_policy.h"
 #include "chrome/browser/font_family_cache.h"
 #include "chrome/browser/geolocation/chrome_access_token_store.h"
 #include "chrome/browser/media/media_capture_devices_dispatcher.h"
@@ -1918,6 +1919,14 @@ ChromeContentBrowserClient::CreateQuotaPermissionContext() {
   return new ChromeQuotaPermissionContext();
 }
 
+scoped_ptr<storage::QuotaEvictionPolicy>
+ChromeContentBrowserClient::GetTemporaryStorageEvictionPolicy(
+    content::BrowserContext* context) {
+  return SiteEngagementEvictionPolicy::IsEnabled()
+             ? make_scoped_ptr(new SiteEngagementEvictionPolicy(context))
+             : nullptr;
+}
+
 void ChromeContentBrowserClient::AllowCertificateError(
     int render_process_id,
     int render_frame_id,