Cleanup handles more efficiently, ensures we don't have to iterate over them

runtime/vm/handles_impl.h

 // 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.
 
 #ifndef VM_HANDLES_IMPL_H_
 #define VM_HANDLES_IMPL_H_
 
 #include "vm/heap.h"
 #include "vm/heap_trace.h"
 #include "vm/visitor.h"
@@ skipping 20 matching lines @@
 
 
 template <int kHandleSizeInWords, int kHandlesPerChunk, int kOffsetOfRawPtr>
 void Handles<kHandleSizeInWords,
              kHandlesPerChunk,
              kOffsetOfRawPtr>::VisitScopedHandles(
     ObjectPointerVisitor* visitor) {
   HandlesBlock* block = &first_scoped_block_;
   do {
     block->VisitObjectPointers(visitor);
+    if (block == scoped_blocks_) {
+      return;
+    }
     block = block->next_block();
   } while (block != NULL);
+  UNREACHABLE();
 }
 
 
 template <int kHandleSizeInWords, int kHandlesPerChunk, int kOffsetOfRawPtr>
 void Handles<kHandleSizeInWords,
              kHandlesPerChunk,
              kOffsetOfRawPtr>::VisitUnvisitedScopedHandles(
     ObjectPointerVisitor* visitor) {
   HandlesBlock* block = &first_scoped_block_;
   while (block != NULL && block != last_visited_block_) {
@@ skipping 336 matching lines @@
 template <int kHandleSizeInWords, int kHandlesPerChunk, int kOffsetOfRawPtr>
 int Handles<kHandleSizeInWords,
             kHandlesPerChunk,
             kOffsetOfRawPtr>::HandlesBlock::HandleCount() const {
   return (next_handle_slot_ / kHandleSizeInWords);
 }
 
 }  // namespace dart
 
 #endif  // VM_HANDLES_IMPL_H_