Remove more uses of Isolate::current_zone.

Remove more uses of Isolate::current_zone.

The most substantial change is in Parser and ParsedFunction, which now cache their calling thread. (A similar change was tried unsuccessfully in the past, but can now be safely implemented thanks to the ThreadRegistry state saving.)

Only remaining users are the Object::Handle(Isolate*, [...]) methods. Then, this deprecated interface will be removed.

BUG=
R=asiva@google.com

Committed: https://github.com/dart-lang/sdk/commit/700bd543620e38cc336da1c13e7dc69317eb6d31

[koda, 2015-07-20 15:43:34]

koda@google.com changed reviewers:
+ asiva@google.com

[siva, 2015-07-21 15:47:20]

LGTM with one comment.

https://codereview.chromium.org/1242343002/diff/1/runtime/vm/parser.h
File runtime/vm/parser.h (right):

https://codereview.chromium.org/1242343002/diff/1/runtime/vm/parser.h#newcode814
runtime/vm/parser.h:814: Isolate* isolate_;  // Cached current isolate.
Do you need to cache the current isolate like this?

Can we have :

Isolate* isolate() const { return thread_->isolate(); }

[koda, 2015-07-21 16:29:29]

https://codereview.chromium.org/1242343002/diff/1/runtime/vm/parser.h
File runtime/vm/parser.h (right):

https://codereview.chromium.org/1242343002/diff/1/runtime/vm/parser.h#newcode814
runtime/vm/parser.h:814: Isolate* isolate_;  // Cached current isolate.
On 2015/07/21 15:47:20, siva wrote:
> Do you need to cache the current isolate like this?
> 
> Can we have :
> 
> Isolate* isolate() const { return thread_->isolate(); }

Done.

[koda, 2015-07-21 16:37:29]

Committed patchset #2 (id:20001) manually as
700bd543620e38cc336da1c13e7dc69317eb6d31 (presubmit successful).