Reland r17907 - Make it possible to add more than one piece of embedder data to isolates"

Reland r17907 - Make it possible to add more than one piece of embedder data to isolates"

This will allow for using gin and blink bindings in the same
process.

Over r17907, I changed the order of fields in Isolate to be stable across different platforms, since the ABI defined packing is not the same on
all targets, and I initialize the embedder data field in Isolate.

BUG=317398
R=svenpanne@chromium.org, dcarney@chromium.org
LOG=n

Committed: https://code.google.com/p/v8/source/detail?r=17935

[Sven Panne, 2013-11-20 13:54:29]

lgtm

[jochen (gone - plz use gerrit), 2013-11-20 15:16:26]

Committed patchset #3 manually as r17935 (presubmit successful).