add RequestDatum tests and fix some situations

pkg/analysis_server/lib/src/protocol.dart

Index: pkg/analysis_server/lib/src/protocol.dart
diff --git a/pkg/analysis_server/lib/src/protocol.dart b/pkg/analysis_server/lib/src/protocol.dart
index 2c4ecfb258e5aca1dddae53b172134cf60e7ab05..5cdb3af81ff898c99aa6f425b8443e214227b1e1 100644
--- a/pkg/analysis_server/lib/src/protocol.dart
+++ b/pkg/analysis_server/lib/src/protocol.dart
@@ -237,9 +237,9 @@ class RequestDatum {
     if (datum is bool) {
       return datum;
     } else if (datum == 'true') {
-      return datum == 'true';
+      return true;
     } else if (datum == 'false') {
-      return datum == 'false';
+      return false;
     }
     throw new RequestFailure(new Response.invalidParameter(request, datum,
         "be a boolean"));