Add max post-gc heap usage metrics

runtime/vm/pages.cc

Index: runtime/vm/pages.cc
diff --git a/runtime/vm/pages.cc b/runtime/vm/pages.cc
index 7cee6df7868fbd11a1d689a0a364ba9ee601948a..9da3ee24950935fa643ac163015182eb18322041 100644
--- a/runtime/vm/pages.cc
+++ b/runtime/vm/pages.cc
@@ -171,6 +171,7 @@ PageSpace::PageSpace(Heap* heap,
       collections_(0) {
   // We aren't holding the lock but no one can reference us yet.
   UpdateMaxCapacityLocked();
+  UpdateMaxUsed();
 }
 
 
@@ -547,6 +548,33 @@ void PageSpace::UpdateMaxCapacityLocked() {
 }
 
 
+void PageSpace::UpdateMaxUsed() {
+  if (heap_ == NULL) {
+    // Some unit tests.
+    return;
+  }
+  ASSERT(heap_ != NULL);
+  ASSERT(heap_->isolate() != NULL);
+  Isolate* isolate = heap_->isolate();
+  isolate->GetHeapOldUsedMaxMetric()->SetValue(
+      static_cast<int64_t>(UsedInWords()) * kWordSize);
+}
+
+
+void PageSpace::UpdateGlobalMaxUsed() {
+  if (heap_ == NULL) {
+    // Some unit tests.
+    return;
+  }
+  ASSERT(heap_ != NULL);
+  ASSERT(heap_->isolate() != NULL);
+  Isolate* isolate = heap_->isolate();
+  isolate->GetHeapGlobalUsedMaxMetric()->SetValue(
+      (static_cast<int64_t>(heap_->UsedInWords(Heap::kNew)) * kWordSize) +
+      (static_cast<int64_t>(heap_->UsedInWords(Heap::kOld)) * kWordSize));
+}
+
+
 bool PageSpace::Contains(uword addr) const {
   for (ExclusivePageIterator it(this); !it.Done(); it.Advance()) {
     if (it.page()->Contains(addr)) {
@@ -932,6 +960,9 @@ void PageSpace::MarkSweep(bool invoke_api_callbacks) {
     freelist_[HeapPage::kExecutable].Print();
   }
 
+  UpdateMaxUsed();
+  UpdateGlobalMaxUsed();
+
   isolate->thread_registry()->ResumeAllThreads();
 
   // Done, reset the task count.