Handle circular dependencies

[KamranAsif]

http://w3c.github.io/html/infrastructure.html#section-structuredserializeinternal

[KamranAsif]

const foo = {};
foo.name = foo;
const bar = {};
bar.name = bar;

Trivial cases

const source = {prop: foo};
const revision = {prop: foo};

Objects are same reference, so we don't walk down tree.

const source = {prop: foo};
const revision = {prop: [non object/array]};

Both props need to be objects, otherwise we return revision value.

Complex cases

const source = {prop: foo};
const revision = {prop: bar};

Not sure what we should return right now..