Revert: Implement declarative content script API for <webview> [js part].

Revert: Implement declarative content script API for <webview> [js part]:
https://codereview.chromium.org/718203005/

<webview> tag will not support declarative content script API anymore. Instead,
we would like to support dynamically add/remove content scripts,
which are similar to content scripts for Chrome Extension.

BUG=461052
Committed: https://crrev.com/19e4765aa1aa7499dc9a9e35f0090d700f1e377c
Cr-Commit-Position: refs/heads/master@{#318972}

[Xi Han, 2015-03-03 22:24:31]

hanxi@chromium.org changed reviewers:
+ fsamuel@chromium.org

[Xi Han, 2015-03-03 22:24:31]

Hi Fady: PTAL, thanks!

[Fady Samuel, 2015-03-03 22:26:45]

lgtm

[Xi Han, 2015-03-03 22:28:18]

The CQ bit was checked by hanxi@chromium.org

[commit-bot: I haz the power, 2015-03-03 22:28:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/975133002/1

[commit-bot: I haz the power, 2015-03-04 00:14:42]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-04 00:15:19]

Patchset 1 (id:??) landed as
https://crrev.com/19e4765aa1aa7499dc9a9e35f0090d700f1e377c
Cr-Commit-Position: refs/heads/master@{#318972}