Fix the new generation growth criterion so it is not mislead into performing two growths in a row.

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 RUNTIME_VM_SCAVENGER_H_
 #define RUNTIME_VM_SCAVENGER_H_
 
 #include "platform/assert.h"
 #include "platform/utils.h"
 #include "vm/dart.h"
@@ skipping 64 matching lines @@
                 intptr_t promo_candidates_in_words,
                 intptr_t promoted_in_words)
       : start_micros_(start_micros),
         end_micros_(end_micros),
         before_(before),
         after_(after),
         promo_candidates_in_words_(promo_candidates_in_words),
         promoted_in_words_(promoted_in_words) {}
 
   // Of all data before scavenge, what fraction was found to be garbage?
-  double GarbageFraction() const {
+  // If this scavenge included growth, assume the extra capacity would become
+  // garbage to give the scavenger a chance to stablize at the new capacity.
+  double ExpectedGarbageFraction() const {
     intptr_t survived = after_.used_in_words + promoted_in_words_;
-    return 1.0 - (survived / static_cast<double>(before_.used_in_words));
+    return 1.0 - (survived / static_cast<double>(after_.capacity_in_words));
   }
 
   // Fraction of promotion candidates that survived and was thereby promoted.
   // Returns zero if there were no promotion candidates.
   double PromoCandidatesSuccessFraction() const {
     return promo_candidates_in_words_ > 0
                ? promoted_in_words_ /
                      static_cast<double>(promo_candidates_in_words_)
                : 0.0;
   }
@@ skipping 243 matching lines @@
   Mutex* space_lock_;
   friend class ScavengerVisitor;
   friend class ScavengerWeakVisitor;
 
   DISALLOW_COPY_AND_ASSIGN(Scavenger);
 };
 
 }  // namespace dart
 
 #endif  // RUNTIME_VM_SCAVENGER_H_