Revert of Make RenderFrame(Host) own a RenderWidget(Host).

Revert of Make RenderFrame(Host) own a RenderWidget(Host). (patchset #20 id:380001 of https://codereview.chromium.org/616133002/)

Reason for revert:
Speculative revert. After this CL the CrossSiteIframeAccessibility test began failing (build 19379). There was only one other CL in this build and unrelated to iframes.

Original issue's description:
> Make RenderFrame(Host) own a RenderWidget(Host).
>
> When a RenderFrameHost is created for an out-of-process iframe, it
> will create a RenderWidgetHost to manage rendering and input events for
> the iframe and its same-process frame descendants. A corresponding
> RenderWidget is created in the renderer process.
>
> BUG=419087
>
> Committed: https://crrev.com/2dfb76d84f4ebde602c1c3cde700dcf71b4d1bd6
> Cr-Commit-Position: refs/heads/master@{#312451}

TBR=creis@chromium.org,nasko@chromium.org,nick@chromium.org,kenrb@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=419087
Committed: https://crrev.com/04094bf706d970f1fafc94786ec67f511a423d4d
Cr-Commit-Position: refs/heads/master@{#312471}

[cmumford, 2015-01-21 22:03:36]

Created Revert of Make RenderFrame(Host) own a RenderWidget(Host).

[commit-bot: I haz the power, 2015-01-21 22:05:50]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/851333005/1

[commit-bot: I haz the power, 2015-01-21 22:07:58]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-21 22:08:59]

Patchset 1 (id:??) landed as
https://crrev.com/04094bf706d970f1fafc94786ec67f511a423d4d
Cr-Commit-Position: refs/heads/master@{#312471}