Migrate NoSafepointScope; add constrained concurrent allocation to unit test

Migrate NoSafepointScope to Thread, so that helper threads can successfully call Heap::Allocate (but only for old space).

Safepointing is not yet implemented, so helper threads can only allocate when growth control is off and no Dart code is running. But extend unit test to ensure this code path remains exercised as more functionality is added.

BUG=
R=asiva@google.com

Committed: https://github.com/dart-lang/sdk/commit/fc8286ae7131eebb02075f12daa84c0b1dd4abcb

[koda, 2015-07-21 20:02:10]

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

[koda, 2015-07-21 20:06:17]

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

[siva, 2015-07-22 17:52:49]

lgtm

https://codereview.chromium.org/1250463004/diff/60001/runtime/vm/raw_object_s...
File runtime/vm/raw_object_snapshot.cc (right):

https://codereview.chromium.org/1250463004/diff/60001/runtime/vm/raw_object_s...
runtime/vm/raw_object_snapshot.cc:2062:
ASSERT(Thread::Current()->no_safepoint_scope_depth() != 0);
Should this be

reader->isolate()->mutator_thread()->no_safepoint_scope_depth() != 0);

We don't want other thread running this code.

Maybe we can also have another ASSERT

reader->isolate()->AssertCurrentThreadIsMutator();

https://codereview.chromium.org/1250463004/diff/60001/runtime/vm/snapshot.cc
File runtime/vm/snapshot.cc (right):

https://codereview.chromium.org/1250463004/diff/60001/runtime/vm/snapshot.cc#...
runtime/vm/snapshot.cc:612: ASSERT(Thread::Current()->no_safepoint_scope_depth()
!= 0);                  \
Ditto comment about Thread::Current() in this file.

[koda, 2015-07-22 19:55:47]

https://codereview.chromium.org/1250463004/diff/60001/runtime/vm/raw_object_s...
File runtime/vm/raw_object_snapshot.cc (right):

https://codereview.chromium.org/1250463004/diff/60001/runtime/vm/raw_object_s...
runtime/vm/raw_object_snapshot.cc:2062:
ASSERT(Thread::Current()->no_safepoint_scope_depth() != 0);
On 2015/07/22 17:52:49, siva wrote:
> Should this be
> 
> reader->isolate()->mutator_thread()->no_safepoint_scope_depth() != 0);
> 
> We don't want other thread running this code.
> 
> Maybe we can also have another ASSERT
> 
> reader->isolate()->AssertCurrentThreadIsMutator();

I've now added a macro that combines the two assertions (which also unclutters
the code).

Longer term, we might want to support other threads reading snapshots, and we
can update the macro then.

https://codereview.chromium.org/1250463004/diff/60001/runtime/vm/snapshot.cc
File runtime/vm/snapshot.cc (right):

https://codereview.chromium.org/1250463004/diff/60001/runtime/vm/snapshot.cc#...
runtime/vm/snapshot.cc:612: ASSERT(Thread::Current()->no_safepoint_scope_depth()
!= 0);                  \
On 2015/07/22 17:52:49, siva wrote:
> Ditto comment about Thread::Current() in this file.

Done.

[koda, 2015-07-22 22:09:58]

Committed patchset #5 (id:80001) manually as
fc8286ae7131eebb02075f12daa84c0b1dd4abcb (presubmit successful).