Add max post-gc heap usage metrics

runtime/vm/metrics.h

Index: runtime/vm/metrics.h
diff --git a/runtime/vm/metrics.h b/runtime/vm/metrics.h
index 22f9a7895829d5dccff68506dca7d8e06d75695f..9fde2d8870fd14dd53d1fc8c989baf88a5801d95 100644
--- a/runtime/vm/metrics.h
+++ b/runtime/vm/metrics.h
@@ -15,13 +15,17 @@ class JSONStream;
 // Metrics for each isolate.
 #define ISOLATE_METRIC_LIST(V)                                                 \
   V(MetricHeapOldUsed, HeapOldUsed, "heap.old.used", kByte)                    \
+  V(MaxMetric, HeapOldUsedMax, "heap.old.used.max", kByte)                     \
   V(MetricHeapOldCapacity, HeapOldCapacity, "heap.old.capacity", kByte)        \
   V(MaxMetric, HeapOldCapacityMax, "heap.old.capacity.max", kByte)             \
   V(MetricHeapOldExternal, HeapOldExternal, "heap.old.external", kByte)        \
   V(MetricHeapNewUsed, HeapNewUsed, "heap.new.used", kByte)                    \
+  V(MaxMetric, HeapNewUsedMax, "heap.new.used.max", kByte)                     \
   V(MetricHeapNewCapacity, HeapNewCapacity, "heap.new.capacity", kByte)        \
   V(MaxMetric, HeapNewCapacityMax, "heap.new.capacity.max", kByte)             \
-  V(MetricHeapNewExternal, HeapNewExternal, "heap.new.external", kByte)
+  V(MetricHeapNewExternal, HeapNewExternal, "heap.new.external", kByte)        \
+  V(MetricHeapUsed, HeapGlobalUsed, "heap.global.used", kByte)                 \
+  V(MaxMetric, HeapGlobalUsedMax, "heap.global.used.max", kByte)               \
 
 #define VM_METRIC_LIST(V)                                                      \
   V(MetricIsolateCount, IsolateCount, "vm.isolate.count", kCounter)
@@ -166,6 +170,11 @@ class MetricIsolateCount : public Metric {
 };
 
 
+class MetricHeapUsed : public Metric {
+ protected:
+  virtual int64_t Value() const;
+};
+
 }  // namespace dart
 
 #endif  // VM_METRICS_H_