Revert 248827 "android: Migrate old content readback to use asyn..."
Breaks android ToT, and the pairing change downstream is not ready yet.
> android: Migrate old content readback to use async readback (and delegated renderer)
>
> This patch removes the use of a helper context for content readback. Instead,
> we use the async readback API.
>
> This patch is also setting delegated renderer as the default for android.
>
> android= https://chrome-internal-review.googlesource.com/#/c/152377/
>
> BUG=326363
> TBR=sievers
> NOTRY=true
>
> Review URL: https://codereview.chromium.org/
143803004
TBR=powei@chromium.org
Review URL: https://codereview.chromium.org/
149653004
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248976 0039d316-1c4b-4281-b951-d872f2087c98