Merge 176816

Merge 176816
> Enforce non-negative BitstreamBuffer id
> 
> There is some video decode accelerator code that assumes that a negative
> BitstreamBuffer id is never given, and uses it to mark error conditions.
> 
> * Check for non-negative id when receving over IPC.
> * Make sure we don't send negative ids from our video decode pipeline (by
>   handling wrapping)
> * Update PPAPI interface to document the fact that negative ids should not
>   be used.
> 
> BUG=chromium:168293
> TEST=local build, run on snow
> 
> 
> Review URL: https://chromiumcodereview.appspot.com/11826064

TBR=sheu@chromium.org
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=177494