Add ConstantConstructor to ConstantExpression system.

pkg/docgen/lib/src/models/model_helpers.dart

Index: pkg/docgen/lib/src/models/model_helpers.dart
diff --git a/pkg/docgen/lib/src/models/model_helpers.dart b/pkg/docgen/lib/src/models/model_helpers.dart
index 2a7ead3e932b8f94a08fbecf77f7172d3cf36565..7ba9208c6181bff7ab10dc33e21213b7cf5797b9 100644
--- a/pkg/docgen/lib/src/models/model_helpers.dart
+++ b/pkg/docgen/lib/src/models/model_helpers.dart
@@ -79,7 +79,7 @@ class AnnotationInfo {
 }
 
 class AnnotationCreator
-    extends ConstantExpressionVisitor<AnnotationInfo, Annotation> {
+    extends ConstantExpressionVisitor<Annotation, AnnotationInfo> {
 
   const AnnotationCreator();
 
@@ -144,12 +144,6 @@ class AnnotationCreator
   }
 
   @override
-  Annotation visitPrimitive(PrimitiveConstantExpression exp,
-                            AnnotationInfo context) {
-    return null;
-  }
-
-  @override
   Annotation visitSymbol(SymbolConstantExpression exp,
                          AnnotationInfo context) {
     return null;
@@ -172,6 +166,67 @@ class AnnotationCreator
                            AnnotationInfo context) {
     return createAnnotation(exp.element, context);
   }
+
+  @override
+  Annotation visitBool(BoolConstantExpression exp,
+                       AnnotationInfo context) {
+    return null;
+  }
+
+  @override
+  Annotation visitBoolFromEnvironment(BoolFromEnvironmentConstantExpression exp,
+                                      AnnotationInfo context) {
+    return null;
+  }
+
+  @override
+  Annotation visitDouble(DoubleConstantExpression exp,
+                         AnnotationInfo context) {
+    return null;
+  }
+
+  @override
+  Annotation visitInt(IntConstantExpression exp,
+                      AnnotationInfo context) {
+    return null;
+  }
+
+  @override
+  Annotation visitIntFromEnvironment(IntFromEnvironmentConstantExpression exp,
+                                     AnnotationInfo context) {
+    return null;
+  }
+
+  @override
+  Annotation visitNamed(NamedArgumentReference exp,
+                        AnnotationInfo context) {
+    return null;
+  }
+
+  @override
+  Annotation visitNull(NullConstantExpression exp,
+                       AnnotationInfo context) {
+    return null;
+  }
+
+  @override
+  Annotation visitPositional(PositionalArgumentReference exp,
+                             AnnotationInfo context) {
+    return null;
+  }
+
+  @override
+  Annotation visitString(StringConstantExpression exp,
+                         AnnotationInfo context) {
+    return null;
+  }
+
+  @override
+  Annotation visitStringFromEnvironment(
+      StringFromEnvironmentConstantExpression exp,
+      AnnotationInfo context) {
+    return null;
+  }
 }
 
 /// A declaration is private if itself is private, or the owner is private.