Use ElementAnnotation as the ConstantEvaluationTarget for annotations.

pkg/analyzer/lib/src/dart/element/element.dart

Index: pkg/analyzer/lib/src/dart/element/element.dart
diff --git a/pkg/analyzer/lib/src/dart/element/element.dart b/pkg/analyzer/lib/src/dart/element/element.dart
index 11dc96c7d2d2713166a18d3a2333849427b8eb49..02d0fa107d6991f4f5a1e409d6e9df0cae39f4bb 100644
--- a/pkg/analyzer/lib/src/dart/element/element.dart
+++ b/pkg/analyzer/lib/src/dart/element/element.dart
@@ -1573,7 +1573,13 @@ class ElementAnnotationImpl implements ElementAnnotation {
   /**
    * The compliation unit in which this annotation appears.
    */
-  final CompilationUnitElement compilationUnit;
+  final CompilationUnitElementImpl compilationUnit;
+
+  /**
+   * The AST of the annotation itself, cloned from the resolved AST for the
+   * source code.
+   */
+  Annotation annotationAst;
 
   /**
    * The result of evaluating this annotation as a compile-time constant
@@ -1592,6 +1598,9 @@ class ElementAnnotationImpl implements ElementAnnotation {
   DartObject get constantValue => evaluationResult.value;
 
   @override
+  AnalysisContext get context => compilationUnit.library.context;
+
+  @override
   bool get isDeprecated {
     if (element != null) {
       LibraryElement library = element.library;
@@ -1639,6 +1648,14 @@ class ElementAnnotationImpl implements ElementAnnotation {
     return false;
   }
 
+  /**
+   * Get the library containing this annotation.
+   */
+  Source get librarySource => compilationUnit.librarySource;
+
+  @override
+  Source get source => compilationUnit.source;
+
   @override
   String toString() => '@$element';
 }
@@ -4111,8 +4128,8 @@ class ParameterElementImpl extends VariableElementImpl
   /**
    * Creates a synthetic parameter with [name], [type] and [kind].
    */
-  factory ParameterElementImpl.synthetic(String name, DartType type,
-      ParameterKind kind) {
+  factory ParameterElementImpl.synthetic(
+      String name, DartType type, ParameterKind kind) {
     ParameterElementImpl element = new ParameterElementImpl(name, -1);
     element.type = type;
     element.synthetic = true;