Remove a bunch of Isolate::UncheckedCurrent calls

Remove a bunch of Isolate::UncheckedCurrent calls

The callbacks are per isolate, so we shouldn't get the isolate implicitly
from TLS. Also, we shouldn't allow calls to these methods prior to
initializing the respective isolate (and silently ignore them).

Esp. add a per-isolate API to set the stats counter callbacks and
make it possible to set the stats counter callback after the isolate
was touched.

Embedders should use e.g. isolate->SetCounterFunction(callback) instead
of v8::V8::SetCounterFunction(callback).

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

Committed: https://code.google.com/p/v8/source/detail?r=22223

[Sven Panne, 2014-07-07 06:50:18]

LGTM with nits. Furthermore, a short explanation *why* this is beneficial should
be in the CL description, making our a API change description docs easier to
write.

https://codereview.chromium.org/365153002/diff/20001/include/v8.h
File include/v8.h (right):

https://codereview.chromium.org/365153002/diff/20001/include/v8.h#newcode4763
include/v8.h:4763: * Deprecated, will be removed.
I think that

   Deprecated, use Isolate::SetCounterFunction instead.

would be more helpful.

https://codereview.chromium.org/365153002/diff/20001/include/v8.h#newcode4773
include/v8.h:4773: * Deprecated, will be removed.
Same here.

https://codereview.chromium.org/365153002/diff/20001/include/v8.h#newcode4776
include/v8.h:4776: static void
SetAddHistogramSampleFunction(AddHistogramSampleCallback);
Missing deprecation comment.

[jochen (gone - plz use gerrit), 2014-07-07 07:20:16]

Committed patchset #2 manually as r22223 (presubmit successful).