Disable PrecacheLauncher and ExternalPrerenderHandler tests on svelte

Disable PrecacheLauncher and ExternalPrerenderHandler tests on svelte

These tests depend on prerender feature which is disabled on svelte devices.

BUG=529490
Committed: https://crrev.com/5c92b7e76b8c09fc7f79d0ddc01ceda4a3e3a3c4
Cr-Commit-Position: refs/heads/master@{#347853}

[Yusuf, 2015-09-08 23:57:35]

yusufo@chromium.org changed reviewers:
+ tedchoc@chromium.org

[Yusuf, 2015-09-08 23:57:39]

The CQ bit was checked by yusufo@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-09-08 23:57:59]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1305063010/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1305063010/1

[Yusuf, 2015-09-09 00:07:35]

The CQ bit was checked by yusufo@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-09-09 00:07:58]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1305063010/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1305063010/20001

[Yusuf, 2015-09-09 00:09:02]

Patchset #2 (id:20001) has been deleted

[Ted C, 2015-09-09 00:09:26]

lgtm

[twifkak, 2015-09-09 00:29:24]

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

[twifkak, 2015-09-09 00:29:25]

lgtm

[commit-bot: I haz the power, 2015-09-09 00:39:51]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-09 00:39:52]

Dry run: This issue passed the CQ dry run.

[Yusuf, 2015-09-09 00:54:54]

The CQ bit was checked by yusufo@chromium.org

[commit-bot: I haz the power, 2015-09-09 00:55:29]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1305063010/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1305063010/1

[commit-bot: I haz the power, 2015-09-09 01:02:35]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-09 01:03:41]

Patchset 1 (id:??) landed as
https://crrev.com/5c92b7e76b8c09fc7f79d0ddc01ceda4a3e3a3c4
Cr-Commit-Position: refs/heads/master@{#347853}