Bug 1368302 - stylo: possible stack overflow when processing very deep DOM.  r=bholley.
Bug 1368302 - stylo: possible stack overflow when processing very deep DOM.  r=bholley.

Whilst working with variants of the bloom-basic test for Stylo perf
profiling, I noticed that it is easy to cause Firefox to segfault on DOMs
with a depth of more than about 1500 elements.  This fix limits the use of
tail recursion to 150 elements.  This isn't externally observable to content
-- we're still completely correct, just not using tail recursion any more.

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