Fix error handling in analysis.getError.

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 cf522fbd7f16d828243539e154e665716614e0de..8979113ca9f17907c392dd9caac2170e51f9234c 100644
--- a/pkg/analysis_server/test/integration/integration_test_methods.dart
+++ b/pkg/analysis_server/test/integration/integration_test_methods.dart
@@ -172,6 +172,11 @@ abstract class IntegrationTestMixin {
    * as it becomes available should use the information provided by the
    * 'analysis.errors' notification.
    *
+   * 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_ERRORS_INVALID_FILE will be generated.
+   *
    * Parameters
    *
    * file ( FilePath )