[Cherrypick try #2] Fix computation of runtime for throttled tasks

[Cherrypick try #2] Fix computation of runtime for throttled tasks

The computation of the delayed task runtime was computing the (virtual)
TimeDomain's now + delay.  That doesn't take into account the skew
between the real time and the virtual time, which meant timers could
run sooner than expected for background tabs.  Timers associated with
foreground tabs are unaffected.

This patch makes the computation of delayed runtime  the responsibility
of the TimeDomain and introduces a ThrottledTimeDomain which computes
the delayed runtime as realtime + delay.

This means timers will no longer run sooner than expected.  Under normal
circumstancs this only timers whose delay modulo 1000ms is less than 100
ms are less likely to be affected.  Timers whose whose delay modulo
1000ms is greater than 900 are highly likely to be affected (there's a
good chance their delay was too small before).

BUG=587074
Review URL: https://codereview.chromium.org/1718233002

Cr-Commit-Position: refs/heads/master@{#376993}
(cherry picked from commit b56bbe4ce3e7276a130a00d83cf00e5672cd6be1)

R=skyostil@chromium.org

Committed: https://chromium.googlesource.com/chromium/src/+/30d9e26c8a397e07d6b2752b1e0ebee09fd8b0fd

[Sami, 2016-03-01 17:13:16]

skyostil@chromium.org changed reviewers:
+ skyostil@chromium.org

[Sami, 2016-03-01 17:13:17]

lgtm (although looks like this could use a git cl format)

[alex clarke (OOO till 29th), 2016-03-01 17:45:12]

Patchset #3 (id:40001) has been deleted

[alex clarke (OOO till 29th), 2016-03-01 17:45:41]

Patchset #3 (id:60001) has been deleted

[alex clarke (OOO till 29th), 2016-03-01 18:10:36]

Description was changed from

==========
[Cherrypick try #2] Fix computation of runtime for throttled tasks

The computation of the delayed task runtime was computing the (virtual)
TimeDomain's now + delay.  That doesn't take into account the skew
between the real time and the virtual time, which meant timers could
run sooner than expected for background tabs.  Timers associated with
foreground tabs are unaffected.

This patch makes the computation of delayed runtime  the responsibility
of the TimeDomain and introduces a ThrottledTimeDomain which computes
the delayed runtime as realtime + delay.

This means timers will no longer run sooner than expected.  Under normal
circumstancs this only timers whose delay modulo 1000ms is less than 100
ms are less likely to be affected.  Timers whose whose delay modulo
1000ms is greater than 900 are highly likely to be affected (there's a
good chance their delay was too small before).

BUG=587074

Review URL: https://codereview.chromium.org/1718233002

Cr-Commit-Position: refs/heads/master@{#376993}
(cherry picked from commit b56bbe4ce3e7276a130a00d83cf00e5672cd6be1)
==========

to

==========
[Cherrypick try #2] Fix computation of runtime for throttled tasks

The computation of the delayed task runtime was computing the (virtual)
TimeDomain's now + delay.  That doesn't take into account the skew
between the real time and the virtual time, which meant timers could
run sooner than expected for background tabs.  Timers associated with
foreground tabs are unaffected.

This patch makes the computation of delayed runtime  the responsibility
of the TimeDomain and introduces a ThrottledTimeDomain which computes
the delayed runtime as realtime + delay.

This means timers will no longer run sooner than expected.  Under normal
circumstancs this only timers whose delay modulo 1000ms is less than 100
ms are less likely to be affected.  Timers whose whose delay modulo
1000ms is greater than 900 are highly likely to be affected (there's a
good chance their delay was too small before).

BUG=587074

Review URL: https://codereview.chromium.org/1718233002

Cr-Commit-Position: refs/heads/master@{#376993}
(cherry picked from commit b56bbe4ce3e7276a130a00d83cf00e5672cd6be1)

R=skyostil@chromium.org

Committed:
https://chromium.googlesource.com/chromium/src/+/30d9e26c8a397e07d6b2752b1e0e...
==========

[alex clarke (OOO till 29th), 2016-03-01 18:10:38]

Committed patchset #3 (id:80001) manually as
30d9e26c8a397e07d6b2752b1e0ebee09fd8b0fd (presubmit successful).