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 a9c79916295aebbe951282d1dd1d33ce3c33d9ba..9a017b6ee9f3beb06fab3528f8412b32317abad9 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"
@@ -1925,6 +1926,14 @@ 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,