Add an integration test for edit.format.

pkg/analysis_server/test/integration/integration_tests.dart

Index: pkg/analysis_server/test/integration/integration_tests.dart
diff --git a/pkg/analysis_server/test/integration/integration_tests.dart b/pkg/analysis_server/test/integration/integration_tests.dart
index 59cbe570f4d8b38a483205bef226d3f910e4d7f2..c45e07fb905a9c580f512fc9a3be40c585edd188 100644
--- a/pkg/analysis_server/test/integration/integration_tests.dart
+++ b/pkg/analysis_server/test/integration/integration_tests.dart
@@ -277,6 +277,11 @@ abstract class AbstractAnalysisServerIntegrationTest
     file.writeAsStringSync(contents);
     return file.resolveSymbolicLinksSync();
   }
+
+  /**
+   * Read a source file with the given absolute [pathname].
+   */
+  String readFile(String pathname) => new File(pathname).readAsStringSync();
 }
 
 /**