Improve type information and minor clean up

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

Index: pkg/analyzer/lib/dart/element/element.dart
diff --git a/pkg/analyzer/lib/dart/element/element.dart b/pkg/analyzer/lib/dart/element/element.dart
index e0a91d93d03bf5e1b094317c178969e1ef2841b7..e7091abbee52977712aace580768e4fcb5054cd6 100644
--- a/pkg/analyzer/lib/dart/element/element.dart
+++ b/pkg/analyzer/lib/dart/element/element.dart
@@ -757,7 +757,8 @@ abstract class Element implements AnalysisTarget {
    * [predicate] returns `true`, or `null` if there is no such ancestor. Note
    * that this element will never be returned.
    */
-  Element getAncestor(Predicate<Element> predicate);
+  Element/*=E*/ getAncestor/*<E extends Element >*/(
+      Predicate<Element> predicate);
 
   /**
    * Return a display name for the given element that includes the path to the
@@ -806,13 +807,6 @@ abstract class ElementAnnotation implements ConstantEvaluationTarget {
   DartObject get constantValue;
 
   /**
-   * Return a representation of the value of this annotation, forcing the value
-   * to be computed if it had not previously been computed, or `null` if the
-   * value of this annotation could not be computed because of errors.
-   */
-  DartObject computeConstantValue();
-
-  /**
    * Return the element representing the field, variable, or const constructor
    * being used as an annotation.
    */
@@ -859,6 +853,13 @@ abstract class ElementAnnotation implements ConstantEvaluationTarget {
    * required.
    */
   bool get isRequired;
+
+  /**
+   * Return a representation of the value of this annotation, forcing the value
+   * to be computed if it had not previously been computed, or `null` if the
+   * value of this annotation could not be computed because of errors.
+   */
+  DartObject computeConstantValue();
 }
 
 /**
@@ -1938,14 +1939,6 @@ abstract class VariableElement implements Element, ConstantEvaluationTarget {
   DartObject get constantValue;
 
   /**
-   * Return a representation of the value of this variable, forcing the value
-   * to be computed if it had not previously been computed, or `null` if either
-   * this variable was not declared with the 'const' modifier or if the value of
-   * this variable could not be computed because of errors.
-   */
-  DartObject computeConstantValue();
-
-  /**
    * Return `true` if this variable element did not have an explicit type
    * specified for it.
    */
@@ -2016,4 +2009,12 @@ abstract class VariableElement implements Element, ConstantEvaluationTarget {
    * 'var').
    */
   DartType get type;
+
+  /**
+   * Return a representation of the value of this variable, forcing the value
+   * to be computed if it had not previously been computed, or `null` if either
+   * this variable was not declared with the 'const' modifier or if the value of
+   * this variable could not be computed because of errors.
+   */
+  DartObject computeConstantValue();
 }