Issue 21419. Don't create navigation region for elements without location.

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

Index: pkg/analysis_server/lib/src/computer/computer_navigation.dart
diff --git a/pkg/analysis_server/lib/src/computer/computer_navigation.dart b/pkg/analysis_server/lib/src/computer/computer_navigation.dart
index f761658d34d8b86d0bbc861fcd2315cf02f11b8d..a21ec59adb80314b1c29f5216ab18da69c590a92 100644
--- a/pkg/analysis_server/lib/src/computer/computer_navigation.dart
+++ b/pkg/analysis_server/lib/src/computer/computer_navigation.dart
@@ -36,6 +36,9 @@ class DartUnitNavigationComputer {
     if (element == null || element == DynamicElementImpl.instance) {
       return;
     }
+    if (element.location == null) {
+      return;
+    }
     protocol.Element target = protocol.newElement_fromEngine(element);
     _regions.add(new protocol.NavigationRegion(offset, length, [target]));
   }