Share const-error messages.

pkg/dart_messages/bin/publish.dart

Index: pkg/dart_messages/bin/publish.dart
diff --git a/pkg/dart_messages/bin/publish.dart b/pkg/dart_messages/bin/publish.dart
index 4b497b8113323e9908a9146240217e04e536399c..acba54f4371238ab979f35e7d29eb5eeb1fe2922 100644
--- a/pkg/dart_messages/bin/publish.dart
+++ b/pkg/dart_messages/bin/publish.dart
@@ -112,17 +112,25 @@ void emitDart2js() {
     }
     if (message.examples != null) {
       out.writeln(",\n    examples: const [");
+
+      String escapeExampleContent(String content) {
+        if (content.contains("\n") || content.contains('"')) {
+          return 'r"""\n$content"""';
+        } else if (content.contains("\\")) {
+          return 'r"$content"';
+        }
+        return '"$content"';
+      }
       for (var example in message.examples) {
         if (example is String) {
-          out.writeln("      r'''");
-          out.write(example);
-          out.write("'''");
+          out.write("      ");
+          out.write(escapeExampleContent(example));
         } else if (example is Map) {
           out.writeln("      const {");
           example.forEach((String fileName, String content) {
-            out.writeln("      '$fileName': r'''");
-            out.write(content);
-            out.writeln("''',");
+            out.writeln("      '$fileName': ");
+            out.write(escapeExampleContent(content));
+            out.writeln(",");
           });
           out.write("      }");
         }