In preparation for caching we store the MathML fragment returned by
local checker. The rational is that the string serialization of the
parse tree is better chachable as the parsetree.
Change-Id: Ice2ef1f4f7b83ed187507d4d067f446603d0d6a5
In native MathML we only display MathML, also get
rid of enclosing <div / <span container.
Bug: T182041
Change-Id: I26bc4ea88d360d53cc7a34a89bef78812b84b2ea