PPAPI: Refactor MessageChannel to prep for sync postMessage
1) Remove unused CopyPPVar function from MessageChannel
2) Remove mostly-duplicate NPVariantToPPVar from MessageChannel.
3) Separate V8VarConverter::FromV8Value implementation from calling the callback (so I can have a sync path later, and this is shorter anyway).
4) Simplify NaCl in-process to out-of-process transition. Now, we just queue stuff for in-process (nobody but NaCl uses Messaging in-process), and if/when we switch to out-of-process (handing off to a NaCl app) we drain the queues then.
5) Some other renames/tweaks to how MessageChannel queues pending conversions.
BUG=367896
R=raymes@chromium.org
Review URL: https://codereview.chromium.org/
290553004
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@272583 0039d316-1c4b-4281-b951-d872f2087c98