Revert of Revert of Migrate accessibility from RenderView to RenderFrame.

Revert of Revert of Migrate accessibility from RenderView to RenderFrame. (https://codereview.chromium.org/407493002/)

Reason for revert:
Reverting the revert. This didn't break the tree; it's still broken without the patch. :(

Sorry for the noise!

Original issue's description:
> Revert of Migrate accessibility from RenderView to RenderFrame. (https://codereview.chromium.org/273423004/)
> 
> Reason for revert:
> Speculative revert to fix XP bots.
> 
> XP bots started crashing http://build.chromium.org/p/chromium.win/builders/XP%20Tests%20%281%29/builds/32011 and http://build.chromium.org/p/chromium.win/builders/XP%20Tests%20%282%29/builds/34677
> 
> This CL is the most suspicious in the range. If it doesn't fix the bots, I'll unrevert it.
> 
> Original issue's description:
> > Migrate accessibility from RenderView to RenderFrame and RVH to RFH.
> > 
> > In preparation for out-of-process iframes, move almost all accessibility
> > functionality from RenderView to RenderFrame, and from RVHI and RWHI
> > to RFHI.
> > 
> > In addition, the accessibility mode is moved to WebContents, and changing
> > the mode triggers changing it on all frames.
> > 
> > BUG=368298
> > R=jam@chromium.org, kenrb@chromium.org, nick@chromium.org
> > 
> > Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=283994
> 
> TBR=dmazzoni@chromium.org
> NOTRY=true
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=284032

TBR=creis@chromium.org,nick@chromium.org,nasko@chromium.org,jam@chromium.org,dtseng@chromium.org,jschuh@chromium.org,tsepez@chromium.org,kenrb@chromium.org,dmazzoni@chromium.org
NOTREECHECKS=true
NOTRY=true

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=284065

[Mike West, 2014-07-18 12:28:35]

Created Revert of Revert of Migrate accessibility from RenderView to
RenderFrame.

[commit-bot: I haz the power, 2014-07-18 12:29:18]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/mkwst@chromium.org/407493004/1

[commit-bot: I haz the power, 2014-07-18 12:30:50]

Change committed as 284065