Revert of android: Migrate old content readback to use async readback (and delegated renderer) (https://codereview.chromium.org/143803004/)

Reason for revert:
broke android build

Original issue's description:
> 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/153667/
> 
> BUG=326363
> TBR=sievers
> NOTRY=true
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=248827
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=249081

TBR=dtrainor@chromium.org,aelias@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=326363

Review URL: https://codereview.chromium.org/151103010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249175 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249175