Added BASE_EXPORT to EnabledStateObserver class

Added BASE_EXPORT to EnabledStateObserver class

This CL adds a BASE_EXPORT to EnabledStateObserver class. This CL is a
part of the effort to get NetLog data into tracing. Since
EnabledStateObserver is not base exported, we would like it to be so
that we can use it outside base.

BUG=399701
Committed: https://crrev.com/3625753bba5b7097677c9922c71a6557e1772909
Cr-Commit-Position: refs/heads/master@{#293943}

[xunjieli, 2014-09-09 13:44:07]

xunjieli@chromium.org changed reviewers:
+ dsinclair@chromium.org, nduca@chromium.org

[xunjieli, 2014-09-09 13:44:07]

Hi Nat and Dan,

I have moved the BASE_EXPORT change out of CL(536503002) into this new CL. Could
you take a look?

Thanks!
Helen

[dsinclair, 2014-09-09 13:46:48]

lgtm

[dsinclair, 2014-09-09 13:46:55]

The CQ bit was checked by dsinclair@chromium.org

[commit-bot: I haz the power, 2014-09-09 13:47:13]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/xunjieli@chromium.org/551333003/1

[commit-bot: I haz the power, 2014-09-09 15:40:39]

Committed patchset #1 (id:1) as c7a868dace358049c94a35b08585cc2617a85789

[commit-bot: I haz the power, 2014-09-10 03:53:30]

Patchset 1 (id:??) landed as
https://crrev.com/3625753bba5b7097677c9922c71a6557e1772909
Cr-Commit-Position: refs/heads/master@{#293943}