Make XMLDocumentParser disable libxml's support for catalog files.

This fixes some age-old stderr and stdout spew when running the tests.

This should have no effect for users.  Embedders of Blink which happen
to use catalog files (I doubt such an embedder exists) will no longer
be able to do so (since libxml settings are process-global).

BUG=277834
R=abarth

Review URL: https://chromiumcodereview.appspot.com/23102012

git-svn-id: svn://svn.chromium.org/blink/trunk@156606 bbb929c8-8fbe-4397-9dbb-9b2b20218538