Fix pretty printing of QualifiedName in gdb

The structure of QualifiedName was chnaged, and now we need to update the
gdb pretty printer.

BUG=

Review URL: https://codereview.chromium.org/139993003

git-svn-id: svn://svn.chromium.org/blink/trunk@165252 bbb929c8-8fbe-4397-9dbb-9b2b20218538