Migrate NoSafepointScope; add constrained concurrent allocation to unit test

runtime/vm/heap_test.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/globals.h"
 
 #include "platform/assert.h"
 #include "vm/dart_api_impl.h"
 #include "vm/globals.h"
 #include "vm/heap.h"
@@ skipping 195 matching lines @@
   EXPECT_LE(expected_size, after - before);
   EXPECT_GT(expected_size + kTolerance, after - before);
   Dart_ExitScope();
 }
 
 
 class FindOnly : public FindObjectVisitor {
  public:
   FindOnly(Isolate* isolate, RawObject* target)
       : FindObjectVisitor(isolate), target_(target) {
-    ASSERT(isolate->no_safepoint_scope_depth() != 0);
+#if defined(DEBUG)
+    EXPECT_GT(Thread::Current()->no_safepoint_scope_depth(), 0);
+#endif
   }
   virtual ~FindOnly() { }
 
   virtual bool FindObject(RawObject* obj) const {
     return obj == target_;
   }
  private:
   RawObject* target_;
 };
 
@@ skipping 30 matching lines @@
   const String& obj = String::Handle(String::New("x", Heap::kOld));
   Heap* heap = Thread::Current()->isolate()->heap();
   EXPECT(heap->Contains(RawObject::ToAddr(obj.raw())));
   heap->WriteProtect(true);
   EXPECT(heap->Contains(RawObject::ToAddr(obj.raw())));
   heap->WriteProtect(false);
   EXPECT(heap->Contains(RawObject::ToAddr(obj.raw())));
 }
 
 }  // namespace dart.