Remove shouldPersist from WebPlugin.h.

The only caller of shouldPersist was removed in r201401. This removes the
method from the WebPlugin API.

BUG=370459

Review URL: https://codereview.chromium.org/1358123002

git-svn-id: svn://svn.chromium.org/blink/trunk/public@202635 bbb929c8-8fbe-4397-9dbb-9b2b20218538
1 file changed