Implement a garbage collection prologue and epilogue callback mechanism.

runtime/vm/gc_marker.cc

 // Copyright (c) 2011, 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 "vm/gc_marker.h"
 
 #include "vm/allocation.h"
 #include "vm/dart_api_state.h"
 #include "vm/isolate.h"
 #include "vm/pages.h"
@@ skipping 201 matching lines @@
       WeakPersistentHandle::Finalize(handle);
     }
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(MarkingWeakVisitor);
 };
 
 
 void GCMarker::Prologue(Isolate* isolate) {
-  // Nothing to do at the moment.
+  // Always invoke the prologue callbacks.
+  isolate->gc_prologue_callbacks().Invoke();
 }
 
 
+void GCMarker::Epilogue(Isolate* isolate) {
+  // Always invoke the epilogue callbacks.
+  isolate->gc_epilogue_callbacks().Invoke();
+}
+
+
 void GCMarker::IterateRoots(Isolate* isolate, ObjectPointerVisitor* visitor) {
   isolate->VisitObjectPointers(visitor,
                                StackFrameIterator::kDontValidateFrames);
   heap_->IterateNewPointers(visitor);
   heap_->IterateCodePointers(visitor);
 }
 
 
 void GCMarker::IterateWeakRoots(Isolate* isolate, HandleVisitor* visitor) {
   isolate->VisitWeakPersistentHandles(visitor);
@@ skipping 62 matching lines @@
 
 void GCMarker::MarkObjects(Isolate* isolate, PageSpace* page_space) {
   MarkingStack marking_stack;
   Prologue(isolate);
   MarkingVisitor mark(heap_, page_space, &marking_stack);
   IterateRoots(isolate, &mark);
   DrainMarkingStack(isolate, &mark);
   IterateWeakReferences(isolate, &mark);
   MarkingWeakVisitor mark_weak;
   IterateWeakRoots(isolate, &mark_weak);
+  Epilogue(isolate);
 }
 
 }  // namespace dart