Added an Isolate* field to NoTrackDoubleFieldsForSerializerScope, PlatformFeatureScope and BinaryOpIC::State.

The serializer state and even the CPU features will be per-Isolate
later. Currently we get away with global state, because mksnapshot
runs single-threaded and has only 1 Isolate, but this will change.
Furthermore, these changes are yet another prerequisite for removing a
catch-22 at initialization time when we try to enable serialization.

This CL is similar in spirit to r20919, BTW.

BUG=359977
LOG=y
R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/250553005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20963 ce2b1a6d-e550-0410-aec6-3dcde31c8c00