Reland "VM: Handle null-comparisons in the flow graph type propagation"

runtime/vm/object.h

Index: runtime/vm/object.h
diff --git a/runtime/vm/object.h b/runtime/vm/object.h
index 0314d770120306de871a98e63cb2b55bb1f069fe..6c5510bf52eea948bac00c77a5453fd4280f807f 100644
--- a/runtime/vm/object.h
+++ b/runtime/vm/object.h
@@ -5812,6 +5812,9 @@ class AbstractType : public Instance {
   // Check if this type represents the 'int' type.
   bool IsIntType() const;
 
+  // Check if this type represents the '_int64' type.
+  bool IsInt64Type() const;
+
   // Check if this type represents the 'double' type.
   bool IsDoubleType() const;
 
@@ -5966,6 +5969,9 @@ class Type : public AbstractType {
   // The 'int' type.
   static RawType* IntType();
 
+  // The '_int64' type.
+  static RawType* Int64Type();
+
   // The 'Smi' type.
   static RawType* SmiType();