Where: infra/appengine/findit/crash/fracas_parser.py

In FracasParser we repeatedly test whether the priority of the current value of the `callstack` variable is infinity as a way of trying to determine whether the current value of the variable is the same as the initial one. Giving this special meaning to a particular value is confusing and bug-prone; it's better to keep track of a boolean variable on the side to determine whether the current value is still the original one.

Apparently, in the past this design was implemented as a fallback for when the regex in _IsStartOfNewCallStack failed (which would cause the returned `stack_priority` variable to be infinite as well, causing the new callstack object to also satisfy the conditionals, so long as it remains empty). Per katesonia@, it is unclear whether this fallback is still necessary. But even if it is, there should be some more transparent way of implementing the desired behavior.