Migrate NoSafepointScope; add constrained concurrent allocation to unit test

runtime/vm/raw_object_snapshot.cc

Index: runtime/vm/raw_object_snapshot.cc
diff --git a/runtime/vm/raw_object_snapshot.cc b/runtime/vm/raw_object_snapshot.cc
index 057f8e94aad173404a312fd080aead519a4baf17..40a8ac5bc8c043548db03e501a92a67c4444fe4e 100644
--- a/runtime/vm/raw_object_snapshot.cc
+++ b/runtime/vm/raw_object_snapshot.cc
@@ -2059,7 +2059,7 @@ RawOneByteString* OneByteString::ReadFrom(SnapshotReader* reader,
   String& str_obj = String::Handle(reader->zone(), String::null());
 
   if (kind == Snapshot::kFull) {
-    ASSERT(reader->isolate()->no_safepoint_scope_depth() != 0);
+    ASSERT(Thread::Current()->no_safepoint_scope_depth() != 0);

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

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();

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

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.

     RawOneByteString* obj = reader->NewOneByteString(len);
     str_obj = obj;
     str_obj.set_tags(tags);