Add max post-gc heap usage metrics

runtime/vm/pages.h

 // Copyright (c) 2011, 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_PAGES_H_
 #define VM_PAGES_H_
 
 #include "vm/freelist.h"
 #include "vm/globals.h"
 #include "vm/lockers.h"
@@ skipping 216 matching lines @@
      MutexLocker ml(pages_lock_);
      IncreaseCapacityInWordsLocked(increase_in_words);
   }
   void IncreaseCapacityInWordsLocked(intptr_t increase_in_words) {
     DEBUG_ASSERT(pages_lock_->IsOwnedByCurrentThread());
     usage_.capacity_in_words += increase_in_words;
     UpdateMaxCapacityLocked();
   }
 
   void UpdateMaxCapacityLocked();
+  void UpdateMaxUsed();
+  void UpdateGlobalMaxUsed();

[koda, 2015/10/06 18:09:02]

General design comment: Why does the PageSpace/Scavenger need to know about all
the metrics that involve its usage? It would be nice for Heap to just be able to
push a stream of its usage stats to some common place, which then
filters+funnels those values to whatever metrics need updating.

 
   intptr_t ExternalInWords() const {
     return usage_.external_in_words;
   }
   SpaceUsage GetCurrentUsage() const {
     MutexLocker ml(pages_lock_);
     return usage_;
   }
 
   bool Contains(uword addr) const;
@@ skipping 200 matching lines @@
   friend class HeapIterationScope;
   friend class PageSpaceController;
   friend class SweeperTask;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(PageSpace);
 };
 
 }  // namespace dart
 
 #endif  // VM_PAGES_H_