Convert top-level inference errors to hints

pkg/analyzer/lib/src/task/strong/checker.dart

Index: pkg/analyzer/lib/src/task/strong/checker.dart
diff --git a/pkg/analyzer/lib/src/task/strong/checker.dart b/pkg/analyzer/lib/src/task/strong/checker.dart
index 463a5c2ce22853a0ea2babc5a06cd94d1b600e59..aabbfa68d8fd7a63fc12c9853ce3a9fc67323b86 100644
--- a/pkg/analyzer/lib/src/task/strong/checker.dart
+++ b/pkg/analyzer/lib/src/task/strong/checker.dart
@@ -1047,7 +1047,13 @@ class CodeChecker extends RecursiveAstVisitor {
     var severity =
         (processor != null) ? processor.severity : errorCode.errorSeverity;
 
-    if (severity == ErrorSeverity.ERROR) _failure = true;
+    if (errorCode.type == ErrorType.HINT &&
+        errorCode.name.startsWith('STRONG_MODE_TOP_LEVEL_')) {
+      severity = ErrorSeverity.ERROR;
+    }
+    if (severity == ErrorSeverity.ERROR) {
+      _failure = true;

[Leaf, 2017/03/30 19:39:59]

I don't think we want to set _failure for these errors while we're treating
these as hints: otherwise I think DDC may refuse to compile them.  Perhaps put
the previous conditional after this one?

[Brian Wilkerson, 2017/03/30 19:45:18]

Done

+    }
     if (severity != ErrorSeverity.INFO || _options.strongModeHints) {
       int begin = node is AnnotatedNode
           ? node.firstTokenAfterCommentAndMetadata.offset