Add max post-gc heap usage metrics

runtime/vm/scavenger.cc

Index: runtime/vm/scavenger.cc
diff --git a/runtime/vm/scavenger.cc b/runtime/vm/scavenger.cc
index e885b9801e7cf8c877ea03b8abc02333f726927f..83dd9ff66a683542a0dfef265a714df23045e2dd 100644
--- a/runtime/vm/scavenger.cc
+++ b/runtime/vm/scavenger.cc
@@ -415,13 +415,16 @@ Scavenger::Scavenger(Heap* heap,
   if (to_ == NULL) {
     FATAL("Out of memory.\n");
   }
-  UpdateMaxHeapCapacity();
   // Setup local fields.
   top_ = FirstObjectStart();
   resolved_top_ = top_;
   end_ = to_->end();
 
   survivor_end_ = FirstObjectStart();
+
+  UpdateMaxHeapCapacity();
+  UpdateMaxHeapUsage();
+  UpdateGlobalMaxUsed();
 }
 
 
@@ -501,6 +504,8 @@ void Scavenger::Epilogue(Isolate* isolate,
   }
 #endif  // defined(DEBUG)
   from->Delete();
+  UpdateMaxHeapUsage();
+  UpdateGlobalMaxUsed();
   if (invoke_api_callbacks && (isolate->gc_epilogue_callback() != NULL)) {
     (isolate->gc_epilogue_callback())();
   }
@@ -720,6 +725,36 @@ void Scavenger::UpdateMaxHeapCapacity() {
 }
 
 
+void Scavenger::UpdateMaxHeapUsage() {
+  if (heap_ == NULL) {
+    // Some unit tests.
+    return;
+  }
+  ASSERT(to_ != NULL);
+  ASSERT(heap_ != NULL);
+  Isolate* isolate = heap_->isolate();
+  ASSERT(isolate != NULL);
+  isolate->GetHeapNewUsedMaxMetric()->SetValue(UsedInWords() * kWordSize);
+}
+
+
+void Scavenger::UpdateGlobalMaxUsed() {
+  if (heap_ == NULL) {
+    // Some unit tests.
+    return;
+  }
+  ASSERT(to_ != NULL);
+  ASSERT(heap_ != NULL);
+  Isolate* isolate = heap_->isolate();
+  ASSERT(isolate != NULL);
+  // This is technically under-counting, but, we cannot safely query the
+  // page space here. This is also updated whenever a page space GC occurs,
+  // which will reflect the (larger) combined heap usage.
+  isolate->GetHeapGlobalUsedMaxMetric()->SetValue(
+      (static_cast<int64_t>(heap_->UsedInWords(Heap::kNew)) * kWordSize));
+}
+
+
 uword Scavenger::ProcessWeakProperty(RawWeakProperty* raw_weak,
                                      ScavengerVisitor* visitor) {
   // The fate of the weak property is determined by its key.