Add VMMetric and some sample metrics

runtime/vm/isolate.h

Index: runtime/vm/isolate.h
diff --git a/runtime/vm/isolate.h b/runtime/vm/isolate.h
index 041be0644e2ed6a66d0ff3516fd01540b72bc22a..38b529fde68968a14f9e9ae394a5ff936f0e8a3a 100644
--- a/runtime/vm/isolate.h
+++ b/runtime/vm/isolate.h
@@ -13,6 +13,7 @@
 #include "vm/counters.h"
 #include "vm/handles.h"
 #include "vm/megamorphic_cache_table.h"
+#include "vm/metrics.h"
 #include "vm/random.h"
 #include "vm/store_buffer.h"
 #include "vm/tags.h"
@@ -554,12 +555,27 @@ class Isolate : public BaseIsolate {
     return OFFSET_OF(Isolate, current_tag_);
   }
 
+#define ISOLATE_METRIC_ACCESSOR(type, variable, name)                          \
+  type* Get##variable##Metric() { return &vm_metric_##variable##_; }
+  ISOLATE_METRIC_LIST(ISOLATE_METRIC_ACCESSOR);
+#undef ISOLATE_METRIC_ACCESSOR
+
+  static intptr_t IsolateListLength();
+
   RawGrowableObjectArray* tag_table() const { return tag_table_; }
   void set_tag_table(const GrowableObjectArray& value);
 
   RawUserTag* current_tag() const { return current_tag_; }
   void set_current_tag(const UserTag& tag);
 
+  VMMetric* metrics_list_head() {
+    return metrics_list_head_;
+  }
+
+  void set_metrics_list_head(VMMetric* metric) {
+    metrics_list_head_ = metric;
+  }
+
 #if defined(DEBUG)
 #define REUSABLE_HANDLE_SCOPE_ACCESSORS(object)                                \
   void set_reusable_##object##_handle_scope_active(bool value) {               \
@@ -664,6 +680,8 @@ class Isolate : public BaseIsolate {
   RawGrowableObjectArray* tag_table_;
   RawUserTag* current_tag_;
 
+  VMMetric* metrics_list_head_;
+
   Counters counters_;
 
   // Isolate list next pointer.
@@ -682,6 +700,11 @@ class Isolate : public BaseIsolate {
 #undef REUSABLE_HANDLE_SCOPE_VARIABLE
 #endif  // defined(DEBUG)
 
+#define ISOLATE_METRIC_VARIABLE(type, variable, name)                          \
+  type vm_metric_##variable##_;
+  ISOLATE_METRIC_LIST(ISOLATE_METRIC_VARIABLE);
+#undef ISOLATE_METRIC_VARIABLE
+
   VMHandles reusable_handles_;
 
   static Dart_IsolateCreateCallback create_callback_;