Revert of discardable_memory: Using mojo IPC to replace Chrome IPC (patchset #23 id:490001 of https://codereview.chromium.org/2485623002/ )

Reason for revert:
Causing some failures. Example: https://build.chromium.org/p/chromium.chrome/builders/Google%20Chrome%20Mac

Original issue's description:
> discardable_memory: Using mojo IPC to replace Chrome IPC
>
> It also moves ClientDiscardableSharedMemoryManager from ChildThreadImpl
> to RenderThreadImpl and PpapiThread
>
> BUG=654678
>
> Committed: https://crrev.com/a083f971261bcccc53b64e40c911435857ce3bfd
> Cr-Commit-Position: refs/heads/master@{#435969}

TBR=reveman@chromium.org,avi@chromium.org,dcheng@chromium.org,yzshen@chromium.org,sky@chromium.org,penghuang@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=654678

Review-Url: https://codereview.chromium.org/2545523007
Cr-Commit-Position: refs/heads/master@{#435980}
35 files changed