Use entities in impact transformers.

pkg/compiler/lib/src/elements/types.dart

Index: pkg/compiler/lib/src/elements/types.dart
diff --git a/pkg/compiler/lib/src/elements/types.dart b/pkg/compiler/lib/src/elements/types.dart
index f169ef21f0e43b360f7e1573e7c8f30377859aaf..e61b313ce0b764323a69be838e30bdd6aec46619 100644
--- a/pkg/compiler/lib/src/elements/types.dart
+++ b/pkg/compiler/lib/src/elements/types.dart
@@ -62,6 +62,10 @@ abstract class DartType {
 
   /// Whether this type contains a type variable.
   bool get containsTypeVariables => false;
+
+  /// Applies [f] to each occurence of a [ResolutionTypeVariableType] within
+  /// this type.
+  void forEachTypeVariable(f(TypeVariableType variable)) {}
 }
 
 class InterfaceType extends DartType {
@@ -73,6 +77,10 @@ class InterfaceType extends DartType {
   bool get containsTypeVariables =>
       typeArguments.any((type) => type.containsTypeVariables);
 
+  void forEachTypeVariable(f(TypeVariableType variable)) {
+    typeArguments.forEach((type) => type.forEachTypeVariable(f));
+  }
+
   int get hashCode {
     int hash = element.hashCode;
     for (DartType argument in typeArguments) {
@@ -116,6 +124,10 @@ class TypeVariableType extends DartType {
 
   bool get containsTypeVariables => true;
 
+  void forEachTypeVariable(f(TypeVariableType variable)) {
+    f(this);
+  }
+
   int get hashCode => 17 * element.hashCode;
 
   bool operator ==(other) {
@@ -176,6 +188,13 @@ class FunctionType extends DartType {
         namedParameterTypes.any((type) => type.containsTypeVariables);
   }
 
+  void forEachTypeVariable(f(TypeVariableType variable)) {
+    returnType.forEachTypeVariable(f);
+    parameterTypes.forEach((type) => type.forEachTypeVariable(f));
+    optionalParameterTypes.forEach((type) => type.forEachTypeVariable(f));
+    namedParameterTypes.forEach((type) => type.forEachTypeVariable(f));
+  }
+
   bool get isFunctionType => true;
 
   int get hashCode {