perf: Make RAF heavy first frame test do what it says

perf: Make RAF heavy first frame test do what it says

The requestAnimationFrame test which simulates a large jank in the
first rAF callback (raf.html?heavy_first_frame) was actually adding
the delay to every callback. This patch fixes the synthetic delay
to use the correct one-shot mode.

BUG=391005
Committed: https://crrev.com/ca0fe2ef7016eefc24bd860d25566a9f1577a8c1
Cr-Commit-Position: refs/heads/master@{#291886}

[brianderson, 2014-08-22 18:11:35]

lgtm

[Sami, 2014-08-26 09:17:43]

The CQ bit was checked by skyostil@chromium.org

[commit-bot: I haz the power, 2014-08-26 09:18:47]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/skyostil@chromium.org/497173002/1

[commit-bot: I haz the power, 2014-08-26 10:18:47]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  android_clang_dbg on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_clang_d...)

[commit-bot: I haz the power, 2014-08-26 11:31:47]

Committed patchset #1 (1) as fdf168ae0df697b5d19a7a76538c9cedaf45a9e9

[commit-bot: I haz the power, 2014-09-10 02:42:11]

Patchset 1 (id:??) landed as
https://crrev.com/ca0fe2ef7016eefc24bd860d25566a9f1577a8c1
Cr-Commit-Position: refs/heads/master@{#291886}