Fix crashes in ElementsUploadDataStreamTest

Fix crashes in ElementsUploadDataStreamTest

standard lib reports:
error: attempt to insert with an iterator range
[__first, __last) from this container.

When compiling standard lib from gcc 4.9 with C++11, insert
cannot take the same vector as both source and destination.

BUG=None

Committed: https://crrev.com/190d3252e6a748150527da946eda704a6a30894d
Cr-Commit-Position: refs/heads/master@{#307699}

[haavardm, 2014-12-09 21:06:17]

haavardm@opera.com changed reviewers:
+ pauljensen@chromium.org

[haavardm, 2014-12-09 21:27:10]

I've updated to ubuntu 14.10 with new libraries, which probably explains why I'm
among the first to get this crash.

[pauljensen, 2014-12-10 14:08:26]

lgtm

[haavardm, 2014-12-10 14:17:00]

The CQ bit was checked by haavardm@opera.com

[commit-bot: I haz the power, 2014-12-10 14:17:50]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/789953002/1

[commit-bot: I haz the power, 2014-12-10 14:59:50]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-12-10 15:01:15]

Patchset 1 (id:??) landed as
https://crrev.com/190d3252e6a748150527da946eda704a6a30894d
Cr-Commit-Position: refs/heads/master@{#307699}