Revert 181950 - Broke content_unittests on Android

Revert 181950 - Broke content_unittests on Android
> Distribute extra memory evenly among visible clients
> 
> After computing all clients' memory budgets, take any
> extra memory left over and distribute it amongst the
> visible clients (so that, if their memory requirments
> suddenly jump, they don't need to wait for a roundtrip
> to the GPU process to get extra memory).
> 
> Disallow keeping around backgrounded tabs' contents on
> Android, to keep the maximum for the main tab.
> 
> Explicitly limit the memory to use for prepainting by
> specifying NiceToHave on Mac to avoid performance problems.
> 
> BUG=175125
> 
> Review URL: https://codereview.chromium.org/12226082

TBR=ccameron@chromium.org
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=181962