Introducing a net::GenerateMimeMultipartBoundary helper.

net/base/mime_util.h

Index: net/base/mime_util.h
diff --git a/net/base/mime_util.h b/net/base/mime_util.h
index d58ddb07a92ba9ee9d85c5fd358a6ddec7aa8a96..48b9a648af696a9307f6f85b1fe427dc92eecae9 100644
--- a/net/base/mime_util.h
+++ b/net/base/mime_util.h
@@ -100,6 +100,10 @@ enum CertificateMimeType {
   CERTIFICATE_MIME_TYPE_PKCS12_ARCHIVE,
 };
 
+// Generates a random MIME multipart boundary.
+// The returned string is guaranteed to be at most 70 characters long.
+NET_EXPORT std::string GenerateMimeMultipartBoundary();
+
 // Prepares one value as part of a multi-part upload request.
 NET_EXPORT void AddMultipartValueForUpload(const std::string& value_name,
                                            const std::string& value,