Avoid copying the data string when posting ImportantFileWriter write tasks

Avoid copying the data string when posting ImportantFileWriter write tasks

When binding the data string to a callback, the existing code copies the data which can be 1MB+ sometimes.
Use scoped_ptr to avoid unnecessary data copy.

BUG=None

Committed: https://crrev.com/1ad9bfe4e302fd57bbffd45ec9ad248893a7b2ba
Cr-Commit-Position: refs/heads/master@{#327234}

[hashimoto, 2015-04-27 05:00:38]

hashimoto@chromium.org changed reviewers:
+ thakis@chromium.org

[Nico, 2015-04-27 17:53:59]

lgtm

(I was a bit skeptical about this, but since there seem to be very few callers
and it works well for them, this is ok)

[hashimoto, 2015-04-28 03:49:27]

hashimoto@chromium.org changed reviewers:
+ sky@chromium.org

[hashimoto, 2015-04-28 03:49:41]

TBRing sky@ as an owner of components/bookmarks.

[hashimoto, 2015-04-28 03:49:44]

The CQ bit was checked by hashimoto@chromium.org

[commit-bot: I haz the power, 2015-04-28 03:49:54]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1079943002/1

[sky, 2015-04-28 04:23:47]

LGTM

[hashimoto, 2015-04-28 04:29:27]

On 2015/04/28 04:23:47, sky wrote:
> LGTM

Thanks, removing the TBR line from the change description.

[commit-bot: I haz the power, 2015-04-28 05:27:27]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-28 05:28:22]

Patchset 1 (id:??) landed as
https://crrev.com/1ad9bfe4e302fd57bbffd45ec9ad248893a7b2ba
Cr-Commit-Position: refs/heads/master@{#327234}