Partially reland r131930. Only assert on system context leaks this time.

Partially reland r131930. Only assert on system context leaks this time.

Original CL:
==========
Assert we do not leak requests for the system and safe browsing contexts.

It's possible this will catch some leaks when deployed live. We should be able to analyze the crash dumps and fix the culprits.
==========

This time, I'll only assert we do not leak requests for the system
request context, since I've confirmed that we are leaking requests for
the safe browsing context.

BUG=90971
TEST=None
TBR=eroman


Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=132531

[commit-bot: I haz the power, 2012-04-16 18:22:11]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/willchan@chromium.org/10096017/1

[commit-bot: I haz the power, 2012-04-16 18:55:34]

Try job failure for 10096017-1 (retry) on linux_rel for step "compile" (clobber
build).
It's a second try, previously, step "compile" failed.
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=linux_rel&...

[commit-bot: I haz the power, 2012-04-17 00:32:10]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/willchan@chromium.org/10096017/1

[commit-bot: I haz the power, 2012-04-17 04:35:43]

Change committed as 132531