Issue 23640. Implement 'analysis.getNavigation' request.

pkg/analysis_server/test/integration/integration_test_methods.dart

Index: pkg/analysis_server/test/integration/integration_test_methods.dart
diff --git a/pkg/analysis_server/test/integration/integration_test_methods.dart b/pkg/analysis_server/test/integration/integration_test_methods.dart
index 3b609f2d8d94adc68d6026f5d7228bbd0bc0f830..5794acb52c9ffa4e0798bb06ba3522e31afe4f9f 100644
--- a/pkg/analysis_server/test/integration/integration_test_methods.dart
+++ b/pkg/analysis_server/test/integration/integration_test_methods.dart
@@ -277,6 +277,11 @@ abstract class IntegrationTestMixin {
    * region that starts at the beginning of a line and ends at the end of a
    * (possibly different) line in the file.
    *
+   * If a request is made for a file which does not exist, or which is not
+   * currently subject to analysis (e.g. because it is not associated with any
+   * analysis root specified to analysis.setAnalysisRoots), an error of type
+   * GET_NAVIGATION_INVALID_FILE will be generated.
+   *
    * Parameters
    *
    * file ( FilePath )