Fix DCHECK() firing on GPU bots.

Fix DCHECK() firing on GPU bots.

Looks like the extra frame duration is enough extra leeway to match
a 1-frame cadence if it was previously on the edge.

BUG=439548
TEST=new unittest

Committed: https://crrev.com/326d757e1864bedb122f811e70add8d507d1952c
Cr-Commit-Position: refs/heads/master@{#329914}

[DaleCurtis, 2015-05-14 18:18:29]

dalecurtis@chromium.org changed reviewers:
+ xhwang@chromium.org

[DaleCurtis, 2015-05-14 18:19:58]

xhwang: I believe this is due to floating point precision errors as both my math
and mathematica's Reduce[] function fail to find a solution to the equation:

Reduce[{Ceiling[(d/2)/Abs[r - d]]*r < 8000000, Ceiling[(d/2)/Abs[r - 2*d]]*r >=
8000000, r > 0, d > 0, r < d}, {r, d}]

I'd like to land this ASAP to unblock those bots and add a test afterwards if we
can figure out the right parameters here.

[DaleCurtis, 2015-05-14 18:40:20]

Eh, who cares about math, brute force run over expected intervals and durations
yielded the values necessary :)  Test added.

[DaleCurtis, 2015-05-14 18:56:20]

cc:zmo as an FYI since he's gpu sheriff.

[sandersd (OOO until July 31), 2015-05-14 18:58:51]

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

[sandersd (OOO until July 31), 2015-05-14 18:58:52]

lgtm

[DaleCurtis, 2015-05-14 18:59:14]

The CQ bit was checked by dalecurtis@chromium.org

[commit-bot: I haz the power, 2015-05-14 19:00:26]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1127373006/20001

[xhwang, 2015-05-14 19:29:37]

lgtm

[commit-bot: I haz the power, 2015-05-14 20:02:47]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-05-14 20:03:44]

Patchset 2 (id:??) landed as
https://crrev.com/326d757e1864bedb122f811e70add8d507d1952c
Cr-Commit-Position: refs/heads/master@{#329914}