Persist the scanning state across invocations of ProcessToSpace.

runtime/vm/scavenger.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_SCAVENGER_H_
 #define VM_SCAVENGER_H_
 
 #include "platform/assert.h"
 #include "platform/utils.h"
 #include "vm/flags.h"
@@ skipping 99 matching lines @@
   MemoryRegion* to_;
   MemoryRegion* from_;
 
   Heap* heap_;
 
   // Current allocation top and end. These values are being accessed directly
   // from generated code.
   uword top_;
   uword end_;
 
+  // A pointer to the first unscanned object.  Scanning completes when
+  // this value meets the allocation top.
+  uword resolved_top_;
+
   // Objects below this address have survived a scavenge.
   uword survivor_end_;
 
   // All object are aligned to this value.
   uword object_alignment_;
 
   // Scavenge cycle count.
   int count_;
   // Keep track whether a scavenge is currently running.
   bool scavenging_;
   // Keep track whether the scavenge had a promotion failure.
   bool had_promotion_failure_;
 
   friend class ScavengerVisitor;
   friend class ScavengerWeakVisitor;
 
   DISALLOW_COPY_AND_ASSIGN(Scavenger);
 };
 
 }  // namespace dart
 
 #endif  // VM_SCAVENGER_H_