gyp: fix O(n^2) in dependency calculations.

gyp: fix O(n^2) in dependency calculations.

With 1000 targets an O(n^2) in the dependency management starts to be
noticed. This patch takes a 0.2s function to 0.02s. The function is not
parallelized so this is a true 1% speedup.

Also commented on another *potential* performance problem with very
specific dependency graphs.

BUG=362075
1898

[Daniel Bratell, 2014-04-11 14:08:40]

Another O(n^2) in the dependency code. Nobody imagined a system with 1100+
targets when the code was written I guess.

[scottmg, 2014-04-11 18:28:26]

lgtm

https://codereview.chromium.org/234813003/diff/1/pylib/gyp/input.py
File pylib/gyp/input.py (right):

https://codereview.chromium.org/234813003/diff/1/pylib/gyp/input.py#newcode1483
pylib/gyp/input.py:1483: flat_set = set()
comment here to the effect that _set is for optimization and the two must be
coherent.

[Daniel Bratell, 2014-04-14 12:18:27]

https://codereview.chromium.org/234813003/diff/1/pylib/gyp/input.py
File pylib/gyp/input.py (right):

https://codereview.chromium.org/234813003/diff/1/pylib/gyp/input.py#newcode1483
pylib/gyp/input.py:1483: flat_set = set()
On 2014/04/11 18:28:26, scottmg wrote:
> comment here to the effect that _set is for optimization and the two must be
> coherent.

Done.

[Nico, 2014-04-16 15:34:41]

r1898