add a visualizer for _Ref_count_obj_alloc3 and _Ref_count_obj2 (m…

…icrosoft#2811)

Co-authored-by: Stephan T. Lavavej <stl@nuwen.net>
Co-authored-by: Casey Carter <cartec69@gmail.com>

stl/debugger/STL.natvis

@@ -371,6 +371,14 @@ SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
       </Expand>
   </Type>
 
+  <!-- VS 2019 16.3 -->
+  <Type Name="std::_Ref_count_obj2&lt;*&gt;">
+      <DisplayString>make_shared</DisplayString>
+      <Expand>
+          <Item Condition="_Uses != 0" Name="[original ptr]">($T1 *) &amp;_Storage</Item>
+      </Expand>
+  </Type>
+
   <!-- VC 2015 -->
   <Type Name="std::_Ref_count_obj_alloc&lt;*&gt;">
       <DisplayString>allocate_shared</DisplayString>
@@ -380,6 +388,21 @@ SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
       </Expand>
   </Type>
 
+  <!-- VS 2019 16.7: _Ref_count_obj_alloc3 -->
+  <!-- VS 2019 16.3: _Ref_count_obj_alloc2 -->
+  <Type Name="std::_Ref_count_obj_alloc3&lt;*&gt;">
+      <AlternativeType Name="std::_Ref_count_obj_alloc2&lt;*&gt;" />
+      <!-- stateless allocator -->
+      <Intrinsic Optional="true" Name="allocator" Expression="*((_Mybase *) this)"/>
+      <!-- stateful allocator -->
+      <Intrinsic Optional="true" Name="allocator" Expression="_Myval"/>
+      <DisplayString>allocate_shared</DisplayString>
+      <Expand>
+          <Item Condition="_Uses != 0" Name="[original ptr]">($T1 *) &amp;_Storage</Item>
+          <Item Name="[allocator]">allocator()</Item>
+      </Expand>
+  </Type>
+
   <!-- VC 2017, second toolset update -->
   <Type Name="std::_Ref_count_resource&lt;*&gt;">
       <DisplayString>custom deleter</DisplayString>