Make EqualsIgnoringPrivateKey work with mixin applications.

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index cd65cdca8158940c0080f129c163cdc6c9cc16f1..1faf36f3c21c5b7893a259717d32bccb3ccb5fdf 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -21138,7 +21138,8 @@ static bool EqualsIgnoringPrivateKey(const String& str1, const String& str2) {
 
     if (ch == Library::kPrivateKeySeparator) {
       // Consume a private key separator.
-      while ((pos < len) && (T1::CharAt(str1, pos) != '.')) {
+      while ((pos < len) && (T1::CharAt(str1, pos) != '.') &&
+             (T1::CharAt(str1, pos) != '&')) {
         pos++;
       }
       // Resume matching characters.