don't use internal throwOnWarnings option

pkg/front_end/tool/bazel/worker.dart

Index: pkg/front_end/tool/bazel/worker.dart
diff --git a/pkg/front_end/tool/bazel/worker.dart b/pkg/front_end/tool/bazel/worker.dart
index d7f6adfc2971801d82f2ec8627e591e760f005cd..1dbec8ec4e40ae49ff56f66581131cabcde103c7 100644
--- a/pkg/front_end/tool/bazel/worker.dart
+++ b/pkg/front_end/tool/bazel/worker.dart
@@ -32,7 +32,8 @@ class SummaryWorker extends AsyncWorkerLoop {
     try {
       await computeSummary(request.arguments,
           isWorker: true, outputBuffer: outputBuffer);
-    } catch (_, s) {
+    } catch (e, s) {
+      outputBuffer.writeln(e);
       outputBuffer.writeln(s);
       response.exitCode = 15;
     }
@@ -89,17 +90,17 @@ Future computeSummary(List<String> args,
     ..multiRoots = parsedArgs['multi-root'].map(Uri.parse).toList()
     ..target = new NoneTarget(new TargetFlags());
 
-  if (outputBuffer != null) {
-    options.onError = (CompilationMessage error) {
-      var severityString = severityName(error.severity, capitalized: true);
+  options.onError = (CompilationMessage error) {
+    var severityString = severityName(error.severity, capitalized: true);
+    if (outputBuffer != null) {
       outputBuffer.writeln('$severityString: ${error.message}');
-      if (error.severity != Severity.nit) {
-        throw error;
-      }
-    };
-  } else {
-    options.throwOnWarningsForDebugging = true;
-  }
+    } else {
+      print('$severityString: ${error.message}');
+    }
+    if (error.severity != Severity.nit) {
+      throw error;

[Siggi Cherem (dart-lang), 2017/09/01 17:19:08]

Instead of throwing here, consider setting a boolean that indicates that errors
were seen. Then throw right after `summaryFor`?

That way you can report all errors that come up, and not just the first one.

+    }
+  };
 
   var sources = parsedArgs['source'].map(Uri.parse).toList();
   var program = await summaryFor(sources, options);