Add an optional bound to type parameter references

pkg/kernel/lib/ast.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /// -----------------------------------------------------------------------
 ///                           ERROR HANDLING
 /// -----------------------------------------------------------------------
 ///
 /// As a rule of thumb, errors that can be detected statically are handled by
 /// the frontend, typically by translating the erroneous code into a 'throw' or
@@ skipping 4085 matching lines @@
 
 /// Stores the hash code of function type parameters while computing the hash
 /// code of a [FunctionType] object.
 ///
 /// This ensures that distinct [FunctionType] objects get the same hash code
 /// if they represent the same type, even though their type parameters are
 /// represented by different objects.
 final Map<TypeParameter, int> _temporaryHashCodeTable = <TypeParameter, int>{};
 
 /// Reference to a type variable.
+///
+/// A type variable has an optional bound because type promotion can change the
+/// bound.  A bound of `null` indicates that the bound has not been promoted and
+/// is the same as the [TypeParameter]'s bound.  This allows one to detect
+/// whether the bound has been promoted.
 class TypeParameterType extends DartType {
   TypeParameter parameter;
 
-  TypeParameterType(this.parameter);
+  /// An optional promoted bound on the type parameter.
+  ///
+  /// 'null' indicates that the type parameter's bound has not been promoted and
+  /// is therefore the same as the bound of [parameter].
+  DartType bound;
+
+  TypeParameterType(this.parameter, [this.bound]);
 
   accept(DartTypeVisitor v) => v.visitTypeParameterType(this);
 
   visitChildren(Visitor v) {}
 
   bool operator ==(Object other) {
     return other is TypeParameterType && parameter == other.parameter;
   }
 
   int get hashCode => _temporaryHashCodeTable[parameter] ?? parameter.hashCode;
@@ skipping 354 matching lines @@
 /// typedef has not been assigned a canonical name yet.
 ///
 /// Returns `null` if the typedef is `null`.
 CanonicalName getCanonicalNameOfTypedef(Typedef typedef_) {
   if (typedef_ == null) return null;
   if (typedef_.canonicalName == null) {
     throw '$typedef_ has no canonical name';
   }
   return typedef_.canonicalName;
 }