Issue 28068. Implement diagnostics domain for the new analysis driver.

pkg/analyzer/lib/src/dart/analysis/driver.dart

Index: pkg/analyzer/lib/src/dart/analysis/driver.dart
diff --git a/pkg/analyzer/lib/src/dart/analysis/driver.dart b/pkg/analyzer/lib/src/dart/analysis/driver.dart
index c2865a56fcb6f4260c5be5ab6184f0160eee4c10..2032914c751350435a93d377e95453fed4ac5ab4 100644
--- a/pkg/analyzer/lib/src/dart/analysis/driver.dart
+++ b/pkg/analyzer/lib/src/dart/analysis/driver.dart
@@ -297,6 +297,11 @@ class AnalysisDriver {
   Set<String> get knownFiles => _fsState.knownFilePaths;
 
   /**
+   * Return the number of files scheduled for analysis.
+   */
+  int get numberOfFilesToAnalyze => _filesToAnalyze.length;
+
+  /**
    * Return the list of files that the driver should try to analyze sooner.
    */
   List<String> get priorityFiles => _priorityFiles.toList(growable: false);