Revert of Remove the RenderProcessHost observer and attach the WebContentsObserver earlier to the GuestView.

Revert of Remove the RenderProcessHost observer and attach the WebContentsObserver earlier to the GuestView. (patchset #4 id:60001 of https://codereview.chromium.org/642573002/)

Reason for revert:
Speculative revert for double frees on mac gpu bots.

http://build.chromium.org/p/tryserver.chromium.gpu/builders/mac_gpu_retina_triggered_tests/builds/56935
http://build.chromium.org/p/chromium.gpu/builders/Mac%20Debug%20%28Intel%29/builds/38058

Original issue's description:
> Remove the RenderProcessHost observer and attach the WebContentsObserver earlier to the GuestView.
>
> This fixes an issue where if the embedder WebContents is destroyed during a GuestView creation we may end up leaking the guest WebContents.
>
> BUG=419020
>
> Committed: https://crrev.com/52fce9455ffd688ef3752a816192f9e76555e7d1
> Cr-Commit-Position: refs/heads/master@{#298934}

TBR=fsamuel@chromium.org,lfg@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=419020
Committed: https://crrev.com/08b3992fde2ac62aa98ec0d35e05ce8562288bcc
Cr-Commit-Position: refs/heads/master@{#298974}

[danakj, 2014-10-09 20:38:50]

Created Revert of Remove the RenderProcessHost observer and attach the
WebContentsObserver earlier to the GuestView.