Fix hover documentation for parameters.

pkg/analysis_server/lib/src/computer/computer_hover.dart

Index: pkg/analysis_server/lib/src/computer/computer_hover.dart
diff --git a/pkg/analysis_server/lib/src/computer/computer_hover.dart b/pkg/analysis_server/lib/src/computer/computer_hover.dart
index c09668b73937075f70b217a00996969bfb677548..8d870c099efe51484d03ac38edee23296c778c04 100644
--- a/pkg/analysis_server/lib/src/computer/computer_hover.dart
+++ b/pkg/analysis_server/lib/src/computer/computer_hover.dart
@@ -111,9 +111,7 @@ class DartUnitHoverComputer {
           }
         }
         // documentation
-        String dartDoc = element.computeDocumentationComment();
-        dartDoc = _removeDartDocDelimiters(dartDoc);
-        hover.dartdoc = dartDoc;
+        hover.dartdoc = _computeDocumentation(element);
       }
       // parameter
       hover.parameter = _safeToString(expression.bestParameterElement);
@@ -127,5 +125,13 @@ class DartUnitHoverComputer {
     return null;
   }
 
+  String _computeDocumentation(Element element) {
+    if (element is ParameterElement) {
+      element = element.enclosingElement;
+    }
+    String dartDoc = element.computeDocumentationComment();
+    return _removeDartDocDelimiters(dartDoc);
+  }
+
   static _safeToString(obj) => obj != null ? obj.toString() : null;
 }