Add a virtual destructor to SimpleWebMimeRegistryImpl so that child class destructors get called correctly.
Add a virtual destructor to SimpleWebMimeRegistryImpl so that child class destructors get called correctly.

BUG=62828
TEST=No memory leak in TestShellWebMimeRegistryImpl
Review URL: http://codereview.chromium.org/4880002

git-svn-id: http://src.chromium.org/svn/trunk/src@65967 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 5f46437c595421f69dff5dd76a376a59b8479b98
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser