Add integration tests for the execution domain.

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 d277f2cf0d27efeccd27c5988fd20959a275c151..7f7bd74ca95a8dafe16f0fd3df75888fb51968fd 100644
--- a/pkg/analysis_server/test/integration/integration_tests.dart
+++ b/pkg/analysis_server/test/integration/integration_tests.dart
@@ -577,9 +577,7 @@ class Server {
           _pendingCommands.remove(id);
         }
         if (messageAsMap.containsKey('error')) {
-          // TODO(paulberry): propagate the error info to the completer.
-          completer.completeError(new UnimplementedError(
-              'Server responded with an error: ${JSON.encode(message)}'));
+          completer.completeError(messageAsMap['error']);

[Paul Berry, 2017/02/12 14:39:04]

I'd recommend making a new class which represents an error received from the
server, and contains the error message JSON as a field (perhaps call the class
"ServerErrorMessage").  That way we can catch the specific exception type
without accidentally catching other exceptions.

[devoncarew, 2017/02/12 17:52:34]

Done.

         } else {
           completer.complete(messageAsMap['result']);
         }