Reduce GC from external allocation.

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 142 matching lines @@
                 bool invoke_api_callbacks);
 
   bool IsUnreachable(RawObject** p);
 
   // During a scavenge we need to remember the promoted objects.
   // This is implemented as a stack of objects at the end of the to space. As
   // object sizes are always greater than sizeof(uword) and promoted objects do
   // not consume space in the to space they leave enough room for this stack.
   void PushToPromotedStack(uword addr) {
     ASSERT(scavenging_);
-    ASSERT(external_size_ == 0);
     end_ -= sizeof(addr);
     ASSERT(end_ > top_);
     *reinterpret_cast<uword*>(end_) = addr;
   }
   uword PopFromPromotedStack() {
     ASSERT(scavenging_);
-    ASSERT(external_size_ == 0);
     uword result = *reinterpret_cast<uword*>(end_);
     end_ += sizeof(result);
     ASSERT(end_ <= to_->end());
     return result;
   }
   bool PromotedStackHasMore() const {
     ASSERT(scavenging_);
-    ASSERT(external_size_ == 0);
     return end_ < to_->end();
   }
 
   void ProcessWeakTables();
 
   VirtualMemory* space_;
   MemoryRegion* to_;
   MemoryRegion* from_;
 
   Heap* heap_;
@@ skipping 15 matching lines @@
 
   // Keep track whether a scavenge is currently running.
   bool scavenging_;
   // Keep track whether the scavenge had a promotion failure.
   bool had_promotion_failure_;
 
   int64_t gc_time_micros_;
   intptr_t collections_;
 
   // The total size of external data associated with objects in this scavenger.
-  // External allocations decrease end_. If promoted stack is in use, this is 0.
   intptr_t external_size_;
 
   friend class ScavengerVisitor;
   friend class ScavengerWeakVisitor;
 
   DISALLOW_COPY_AND_ASSIGN(Scavenger);
 };
 
 }  // namespace dart
 
 #endif  // VM_SCAVENGER_H_