Downloads: Avoid some redundant map lookups in DownloadMangerImpl.

Downloads: Avoid some redundant map lookups in DownloadMangerImpl.

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=231469

[Randy Smith (Not in Mondays), 2013-10-25 17:10:38]

LGTM.  

Do you have some evidence that this is actually causing performance problems? 
There are two cases that you've changed that I think were slightly more
comprehensible before the change, but I decided it wasn't a big enough deal to
argue about.  But I'd feel better about this change if there was an actual
performance issue that we were trying to fix.  I don't think of this code as
performance critical, so I've historically biased more towards readability.  But
it's a small enough issue that I'm not too worried about it.

[Lei Zhang, 2013-10-25 22:49:06]

No performance issue concerns. I put back a couple of the ContainsKeys() since
it is more readable.

[Randy Smith (Not in Mondays), 2013-10-28 14:29:30]

Awesome; thanks.  Still LGTM.

[commit-bot: I haz the power, 2013-10-28 18:26:05]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/thestig@chromium.org/41553003/50001

[commit-bot: I haz the power, 2013-10-28 19:12:59]

Retried try job too often on ios_dbg_simulator for step(s) content_unittests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=ios_dbg_si...

[commit-bot: I haz the power, 2013-10-28 20:31:31]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/thestig@chromium.org/41553003/50001

[commit-bot: I haz the power, 2013-10-29 01:07:45]

Change committed as 231469