Rewrite ImplicitConstructorBuilder to use only element model.

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

Index: pkg/analyzer/lib/src/generated/element.dart
diff --git a/pkg/analyzer/lib/src/generated/element.dart b/pkg/analyzer/lib/src/generated/element.dart
index eeb29b2099538191e14cb7a525cd4b62f860b0b9..9a3574cbf59fd2480470cf076fea4a870b75ae56 100644
--- a/pkg/analyzer/lib/src/generated/element.dart
+++ b/pkg/analyzer/lib/src/generated/element.dart
@@ -511,6 +511,11 @@ class ClassElementImpl extends ElementImpl implements ClassElement {
       TypeParameterElementImpl.EMPTY_ARRAY;
 
   /**
+   * The [SourceRange] of the `with` clause, `null` if there is no one.
+   */
+  SourceRange withClauseRange;
+
+  /**
    * Initialize a newly created class element to have the given [name] at the
    * given [offset] in the file that contains the declaration of this element.
    */