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 7213c7b3fbd479893fef88109f3fd703dc7e42e7..fe3538f35a7dfe87d264b33aa72e1784ad7374b4 100644
--- a/content/public/browser/content_browser_client.h
+++ b/content/public/browser/content_browser_client.h
@@ -80,6 +80,7 @@ class SelectFilePolicy;
 namespace storage {
 class ExternalMountPoints;
 class FileSystemBackend;
+class QuotaEvictionPolicy;
 }
 
 namespace content {
@@ -445,6 +446,11 @@ 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
+  // temporary storage.
+  virtual scoped_ptr<storage::QuotaEvictionPolicy>
+  GetTemporaryStorageEvictionPolicy(BrowserContext* context);
+
   // 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