Report malformed URIs in library dependencies

pkg/compiler/lib/src/warnings.dart

Index: pkg/compiler/lib/src/warnings.dart
diff --git a/pkg/compiler/lib/src/warnings.dart b/pkg/compiler/lib/src/warnings.dart
index 1b1272eea532b0145dad665414ee08fd67b79c72..8977b5d9220dfd3a363dbf728a4cec8f805dcfaa 100644
--- a/pkg/compiler/lib/src/warnings.dart
+++ b/pkg/compiler/lib/src/warnings.dart
@@ -1560,6 +1560,17 @@ import 'dart:mirrors';
 main() {}
 """]);
 
+  static const MessageKind INVALID_URI = const MessageKind(
+      "'#{uri}' is not a valid URI.",
+      howToFix: DONT_KNOW_HOW_TO_FIX,
+      examples: const [
+        """
+// can't have a '[' in a URI
+import '../../Udyn[mic ils/expect.dart';
+
+main() {}
+"""]);
+
   static const MessageKind READ_SCRIPT_ERROR = const MessageKind(
       "Can't read '#{uri}' (#{exception}).",
       // Don't know how to fix since the underlying error is unknown.