Revert of [DevTools] Implement DevToolsManager::Observer which notifies about target updates.

Revert of [DevTools] Implement DevToolsManager::Observer which notifies about target updates. (patchset #5 id:80001 of https://codereview.chromium.org/577923002/)

Reason for revert:
Breaks asan bot.
http://build.chromium.org/p/chromium.memory/builders/Linux%20ASan%20LSan%20Tests%20%282%29/builds/7924

Original issue's description:
> [DevTools] Implement DevToolsManager::Observer which notifies about target updates.
>
> BUG=398049
>
> Committed: https://crrev.com/509c17cf55a12b49b017245f6d0cff558f312637
> Cr-Commit-Position: refs/heads/master@{#296921}

TBR=pfeldman@chromium.org,vkuzkokov@chromium.org,jam@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=398049
Committed: https://crrev.com/24ce55da5ac28d3e63cc4427c3d9d71b004c6fbd
Cr-Commit-Position: refs/heads/master@{#296944}

[dgozman, 2014-09-26 15:24:20]

Created Revert of [DevTools] Implement DevToolsManager::Observer which notifies
about target updates.

[commit-bot: I haz the power, 2014-09-26 15:24:58]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/591313006/1

[commit-bot: I haz the power, 2014-09-26 15:25:39]

Committed patchset #1 (id:1) as dc78cf8007cadf247a9cc9c36aab85f8508a2936

[commit-bot: I haz the power, 2014-09-26 15:26:14]

Patchset 1 (id:??) landed as
https://crrev.com/24ce55da5ac28d3e63cc4427c3d9d71b004c6fbd
Cr-Commit-Position: refs/heads/master@{#296944}