Reland 24052 - Require V8 to be explicitly initialized before an Isolate is created

> We also initialize the Isolate on creation.
>
> This should allow for getting rid of the last remaining default isolate
> traces. Also, it'll speed up several isolate related operations that no
> longer require locks.
>
> Embedders that relied on v8::Isolate to return an uninitialized Isolate
> (so they can set ResourceConstraints for example, or set flags that
> modify the way the isolate is created) should either do the setup before
> creating the isolate, or use the recently added CreateParams to pass e.g.
> ResourceConstraints.
>
> BUG=none
> LOG=y
> R=svenpanne@chromium.org
>
> Review URL: https://codereview.chromium.org/469783002

BUG=none
LOG=y
TBR=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/583153002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24067 ce2b1a6d-e550-0410-aec6-3dcde31c8c00