Add support to pass the location of the analysis options file to plugins

pkg/analysis_server/lib/src/plugin/plugin_manager.dart

Index: pkg/analysis_server/lib/src/plugin/plugin_manager.dart
diff --git a/pkg/analysis_server/lib/src/plugin/plugin_manager.dart b/pkg/analysis_server/lib/src/plugin/plugin_manager.dart
index 3f4756bbbd3bb8c20b5a16e3df568514226053a8..d62ede95d07ef46968caeeab77a20cc83e05172c 100644
--- a/pkg/analysis_server/lib/src/plugin/plugin_manager.dart
+++ b/pkg/analysis_server/lib/src/plugin/plugin_manager.dart
@@ -222,8 +222,9 @@ abstract class PluginInfo {
     if (currentSession != null) {
       AnalysisSetContextRootsParams params = new AnalysisSetContextRootsParams(
           contextRoots
-              .map((analyzer.ContextRoot contextRoot) =>
-                  new ContextRoot(contextRoot.root, contextRoot.exclude))
+              .map((analyzer.ContextRoot contextRoot) => new ContextRoot(
+                  contextRoot.root, contextRoot.exclude,
+                  optionsFile: contextRoot.optionsFilePath))
               .toList());
       currentSession.sendRequest(params);
     }