Revert of Proposed alternative for supporting ChromeVox keyboard commands.

Revert of Proposed alternative for supporting ChromeVox keyboard commands. (patchset #8 id:200001 of https://codereview.chromium.org/1185753008/)

Reason for revert:
Appears to be causing crashes. See https://crbug.com/504400.

Original issue's description:
> Proposed alternative for supporting ChromeVox keyboard commands.
>
> ChromeVox, a component extension, has some special use cases not currently supported by the chrome.commands API. Over the past year or so, it has become more clear that these special use cases mean non-trivial changes to the commands API. These changes have also uncovered some bugs due to (a) component extension events and (b) prefs.
>
> This is a proposed simple alternative which still utilizes the same manifest format as the commands API and the same extension listener, but performs its own dispatch. It also need not register accelerators in advance as it hooks into keyboard events via EventRewriter.
>
> This solution has some advantages. It means that we can swap the format and use keys not allowed by the commands API. Also, we can implement more features such as sequencing, or sticky key natively.
>
> Some disadvantages are it will interfere with Chrome OS sticky keys and is Chrome OS specific.
>
> TEST=ensure chrome.commands.onCommand gets called with appropriate command name when keys are struck on OOBE, locked screen, login screen, and logged in.
>
> Committed: https://crrev.com/a97769b865c7a511229d2eee04051d59200bf1b3
> Cr-Commit-Position: refs/heads/master@{#335997}

TBR=dmazzoni@chromium.org,finnur@chromium.org,oshima@chromium.org,sadrul@chromium.org,dtseng@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Committed: https://crrev.com/76d83e95044a4361521fa610c60b8465016e6c8f
Cr-Commit-Position: refs/heads/master@{#336172}

[stevenjb, 2015-06-25 16:31:45]

Created Revert of Proposed alternative for supporting ChromeVox keyboard
commands.

[commit-bot: I haz the power, 2015-06-25 16:34:22]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1211003002/1

[commit-bot: I haz the power, 2015-06-25 16:36:19]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-25 16:37:27]

Patchset 1 (id:??) landed as
https://crrev.com/76d83e95044a4361521fa610c60b8465016e6c8f
Cr-Commit-Position: refs/heads/master@{#336172}