Moved isolate high watermark calculations into the Observatory client.

runtime/vm/isolate.h

Index: runtime/vm/isolate.h
diff --git a/runtime/vm/isolate.h b/runtime/vm/isolate.h
index 3367671ecff81251c63bccd21c86164f780c5b38..dcdf8288c086f3e07125e1dfc5f49093726a1b9b 100644
--- a/runtime/vm/isolate.h
+++ b/runtime/vm/isolate.h
@@ -179,7 +179,6 @@ class Isolate : public BaseIsolate {
 
   ThreadRegistry* thread_registry() const { return thread_registry_; }
   SafepointHandler* safepoint_handler() const { return safepoint_handler_; }
-  uintptr_t memory_high_watermark() const { return memory_high_watermark_; }
   ClassTable* class_table() { return &class_table_; }
   static intptr_t class_table_offset() {
     return OFFSET_OF(Isolate, class_table_);
@@ -692,10 +691,6 @@ class Isolate : public BaseIsolate {
                         bool is_mutator,
                         bool bypass_safepoint = false);
 
-  // Updates the maximum memory usage in bytes of all zones in all threads of
-  // the current isolate.
-  void UpdateMemoryHighWatermark();
-
   // DEPRECATED: Use Thread's methods instead. During migration, these default
   // to using the mutator thread (which must also be the current thread).
   Zone* current_zone() const {
@@ -716,7 +711,6 @@ class Isolate : public BaseIsolate {
 
   ThreadRegistry* thread_registry_;
   SafepointHandler* safepoint_handler_;
-  uintptr_t memory_high_watermark_;
   Dart_MessageNotifyCallback message_notify_callback_;
   char* name_;
   char* debugger_name_;