Stub out tokenizer method for the treebuilder

 * The HTML5 treebuilder interplays with the tokenizer while processing
   certain tokens to change contexts and escaping. The opportunity is long
   since passed in our pipeline.

 * Ex. itwikivoyage/El_Campello?oldid=370746 has an extension that
   returns an iframe.

Bug: 70867
Change-Id: Ic890b4b65d44fbd6d1d8f92f7649f5531ace67bc
Merge "Stub out tokenizer method for the treebuilder"