Report HintCode.UNUSED_ELEMENT for classes.

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

Index: pkg/analyzer/lib/src/generated/element_resolver.dart
diff --git a/pkg/analyzer/lib/src/generated/element_resolver.dart b/pkg/analyzer/lib/src/generated/element_resolver.dart
index e10f99b70b0a8ff1d4a7c9061c811dc863d33a05..886da2a2dc0ae5c91f62823b128ccbfba9802df8 100644
--- a/pkg/analyzer/lib/src/generated/element_resolver.dart
+++ b/pkg/analyzer/lib/src/generated/element_resolver.dart
@@ -1031,6 +1031,7 @@ class ElementResolver extends SimpleAstVisitor<Object> {
       }
     }
     node.staticElement = element;
+    _markElementUsed(element);
     if (node.inSetterContext() && node.inGetterContext() && enclosingClass != null) {
       InterfaceType enclosingType = enclosingClass.type;
       AuxiliaryElements auxiliaryElements = new AuxiliaryElements(_lookUpGetter(null, enclosingType, node.name), null);
@@ -1902,6 +1903,29 @@ class ElementResolver extends SimpleAstVisitor<Object> {
   }
 
   /**
+   * Marks [element] as used in its defining library.
+   */
+  void _markElementUsed(Element element) {
+    // only locally defined elements
+    if (element == null) {
+      return;
+    }
+    if (!identical(element.library, _definingLibrary)) {
+      return;
+    }
+    // convert members to base elements
+    if (element is Member) {
+      element = (element as Member).baseElement;
+    }
+    // ignore references to an element from itself
+    if (identical(element, _resolver.enclosingClass)) {
+      return;
+    }
+    // OK, the element is used
+    (element as ElementImpl).markUsed();
+  }
+
+  /**
    * Given some class element, this method uses [subtypeManager] to find the set of all
    * subtypes; the subtypes are then searched for a member (method, getter, or setter), that matches
    * a passed