Merge 32701 - Don't do work in the SharedIOBuffer constructor; ...

Merge 32701 - Don't do work in the SharedIOBuffer constructor; 

use an Init method instead. This eliminates instances of allocatedbutinvalid SharedIOBuffers. Also clean up some CHECKs and TODOs associated with the bug.

The upshot is that we no longer crash in AsyncResourceHandler::OnResponseCompleted() when we can't allocate shared memory. We now crash (properly, I believe) in the renderer process if the shared memory that failed to allocate was the TransportDIB, since the renderer can't communicate with the browser without it.

BUG=16371
TEST=none 
Review URL: http://codereview.chromium.org/391009

TBR=hawk@chromium.org

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=33126