Add prefetch support to AffiliationBackend.

components/password_manager/core/browser/affiliation_utils.h

Index: components/password_manager/core/browser/affiliation_utils.h
diff --git a/components/password_manager/core/browser/affiliation_utils.h b/components/password_manager/core/browser/affiliation_utils.h
index d7d633d7b1f180d1cde14f237a74d68fdce4529a..1f56c4e8e122aa6dd7f8569aba97fd702f018ce3 100644
--- a/components/password_manager/core/browser/affiliation_utils.h
+++ b/components/password_manager/core/browser/affiliation_utils.h
@@ -106,9 +106,13 @@ class FacetURI {
   bool IsValidAndroidFacetURI() const;
 
   // Returns whether or not this instance represents a valid facet identifier
-  // referring to either a Web or an Android application.
+  // referring to either a Web or an Android application. The empty identfier is
+  // not considered valid.
   bool is_valid() const { return is_valid_; }
 
+  // Returns whether or not this instance represents the empty facet identifier.
+  bool is_empty() const { return canonical_spec_.empty(); }
+
   // Returns the canonical scheme of the encapsulated facet URI, provided it is
   // valid, or the empty string otherwise.
   std::string scheme() const;