Revert of Revert of Add support for deleting non preceeding surrounding text in chrome.input.ime.deleteSurroundingText

Revert of Revert of Add support for deleting non preceeding surrounding text in chrome.input.ime.deleteSurroundingText (patchset #1 id:1 of https://codereview.chromium.org/821233003/)

Reason for revert:
The regression is fixed in the extension code. It should be safe to land this again.

Original issue's description:
> Revert of Add support for deleting non preceeding surrounding text in chrome.input.ime.deleteSurroundingText (patchset #1 id:1 of https://codereview.chromium.org/851333002/)
>
> Reason for revert:
> This cl caused regression that the backspace-to-decommit feature for both VK and physical keyboard autocorrect.
>
> Original issue's description:
> > Add support for deleting non preceeding surrounding text in chrome.input.ime.deleteSurroundingText
> >
> > Previously, only text before cursor will be removed regardless the value of
> > offset. This CL adds support for deleting text after cursor. We want to this
> > feature in order to implement "set existing word to composition mode" feature
> > when cursor is moved inside an existing word. We want to be able to remove the
> > parts of the existing word before cursor and after cursor first and then call
> > setComposition to set the word to composition mode.
> >
> > Note: this API tries to comform the API spec of ibus delete_surrounding_text
> > here: ibus.googlecode.com/svn/docs/ibus-1.5/IBusInputContext.html#IBusInputContext-delete-surrounding-text
> > A noticible difference is a positive offset value in this API does not take effect.
> >
> > BUG=446249
> >
> > Committed: https://crrev.com/756820cb2c42a7b302a16d24909d820ee18dad0e
> > Cr-Commit-Position: refs/heads/master@{#312113}
>
> TBR=nona@chromium.org,bshe@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=446249
>
> Committed: https://crrev.com/7f17a7758881aa33e8790494b170962bc37e05d8
> Cr-Commit-Position: refs/heads/master@{#312304}

TBR=nona@chromium.org,shuchen@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=446249
Committed: https://crrev.com/86f8932a6375da210a30bf7863f73b418443e89f
Cr-Commit-Position: refs/heads/master@{#313076}

[bshe, 2015-01-26 16:09:59]

Created Revert of Revert of Add support for deleting non preceeding surrounding
text in chrome.input.ime.deleteSurroundingText