Add max post-gc heap usage metrics

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/dart.h"
@@ skipping 251 matching lines @@
     end_ += sizeof(result);
     ASSERT(end_ <= to_->end());
     return result;
   }
   bool PromotedStackHasMore() const {
     ASSERT(scavenging_);
     return end_ < to_->end();
   }
 
   void UpdateMaxHeapCapacity();
+  void UpdateMaxHeapUsage();
+  void UpdateGlobalMaxUsed();
 
   void ProcessWeakTables();
 
   intptr_t NewSizeInWords(intptr_t old_size_in_words) const;
 
   // Current allocation top and end. These values are being accessed directly
   // from generated code.
   uword top_;
   uword end_;
 
@@ skipping 26 matching lines @@
 
   friend class ScavengerVisitor;
   friend class ScavengerWeakVisitor;
 
   DISALLOW_COPY_AND_ASSIGN(Scavenger);
 };
 
 }  // namespace dart
 
 #endif  // VM_SCAVENGER_H_