deltas: skip if projected compressed size does not match text size constraint
If we have a delta, we check constraints against a lower bound estimate of the
resulting compressed delta. We then checks this projected size against the ½ⁿ
size constraints. This allows to exclude potential base candidates before doing
any expensive computation.
This only apply to the intermediate-snapshot case since this constraint only apply to
them.
For some pathological cases of a private repository this step provide a
further performance boost (timing from `hg perfrevlogwrite`):
before: 3.145906 seconds
after: 3.010646 seconds
{
// Enforcing
"eqeqeq" : true, // true: Require triple equals (===) for comparison
"forin" : true, // true: Require filtering for..in loops with obj.hasOwnProperty()
"freeze" : true, // true: prohibits overwriting prototypes of native objects such as Array, Date etc.
"nonbsp" : true, // true: Prohibit "non-breaking whitespace" characters.
"undef" : true, // true: Require all non-global variables to be declared (prevents global leaks)
// Environments
"browser" : true // Web Browser (window, document, etc)
}