Use StatsReport::Value::ToString instead of the value member variable direct.

Use StatsReport::Value::ToString instead of the value member variable direct.
This can be landed once the interface change has been made in WebRTC and rolled into Chromium (see here: https://webrtc-codereview.appspot.com/40139004/).

BUG=webrtc:2822
Committed: https://crrev.com/f1eb009c56212783050f9695a42f53bd22e4f3ca
Cr-Commit-Position: refs/heads/master@{#318694}

[tommi (sloooow) - chröme, 2015-03-01 00:45:41]

Rebase

[tommi (sloooow) - chröme, 2015-03-01 15:33:27]

tommi@chromium.org changed reviewers:
+ magjed@chromium.org

[magjed_chromium, 2015-03-02 10:15:03]

lgtm

[tommi (sloooow) - chröme, 2015-03-02 13:09:13]

The CQ bit was checked by tommi@chromium.org

[commit-bot: I haz the power, 2015-03-02 13:09:19]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/875483002/20001

[commit-bot: I haz the power, 2015-03-02 15:23:11]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-03-02 15:24:30]

Patchset 2 (id:??) landed as
https://crrev.com/f1eb009c56212783050f9695a42f53bd22e4f3ca
Cr-Commit-Position: refs/heads/master@{#318694}