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 200 matching lines @@
     bool is_locked = false;
     return TryAllocateInternal(
         size, type, growth_policy, is_protected, is_locked);
   }
 
   bool NeedsGarbageCollection() const {
     return page_space_controller_.NeedsGarbageCollection(usage_) ||
            NeedsExternalGC();
   }
 
-  intptr_t UsedInWords() const { return usage_.used_in_words; }
-  intptr_t CapacityInWords() const {
+  int64_t UsedInWords() const { return usage_.used_in_words; }
+  int64_t CapacityInWords() const {
     MutexLocker ml(pages_lock_);
     return usage_.capacity_in_words;
   }
   void IncreaseCapacityInWords(intptr_t increase_in_words) {
      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();
 
-  intptr_t ExternalInWords() const {
+  int64_t ExternalInWords() const {
     return usage_.external_in_words;
   }
   SpaceUsage GetCurrentUsage() const {
     MutexLocker ml(pages_lock_);
     return usage_;
   }
 
   bool Contains(uword addr) const;
   bool Contains(uword addr, HeapPage::PageType type) const;
   bool IsValidAddress(uword addr) const {
@@ skipping 198 matching lines @@
   friend class HeapIterationScope;
   friend class PageSpaceController;
   friend class SweeperTask;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(PageSpace);
 };
 
 }  // namespace dart
 
 #endif  // VM_PAGES_H_