Rename LocalDataPipe -> LocalDataPipeImpl.

Rename LocalDataPipe -> LocalDataPipeImpl.

This seems a little strange, but it's a step towards the following:
* LocalDataPipeImpl will subclass/implement DataPipeImpl (to be
  introduced) instead of DataPipe.
* DataPipe will have a DataPipeImpl member (instead of being
  subclassed).
* This allows a DataPipe's impl to be swapped out for a different one
  (e.g., a cross-process one). (A DataPipe itself is hard to swap out,
  since Dispatchers have references to it.)

R=yzshen@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/075efe912b678657ab4130999368c70eee2365e9

[viettrungluu, 2015-02-18 23:34:07]

(Now dependent on https://codereview.chromium.org/936173002/.)

[viettrungluu, 2015-02-18 23:34:45]

On 2015/02/18 23:34:07, viettrungluu wrote:
> (Now dependent on https://codereview.chromium.org/936173002/.)

I meant https://codereview.chromium.org/936283002/.

[yzshen1, 2015-02-19 18:02:03]

lgtm

[viettrungluu, 2015-02-19 18:28:56]

New patchsets have been uploaded after l-g-t-m from yzshen@chromium.org

[viettrungluu, 2015-02-19 18:35:00]

Committed patchset #3 (id:40001) manually as
075efe912b678657ab4130999368c70eee2365e9 (presubmit successful).