Add a .gitattributes file to force LF line-endings in net/http/*.pins files.

net/tools/transport_security_state_generator/input_file_parsers.cc

Index: net/tools/transport_security_state_generator/input_file_parsers.cc
diff --git a/net/tools/transport_security_state_generator/input_file_parsers.cc b/net/tools/transport_security_state_generator/input_file_parsers.cc
index 4a633080ed00ec5a830196241985c253babdc411..752969aaa24b0b7a3328cd75af7bc6d09306e4c6 100644
--- a/net/tools/transport_security_state_generator/input_file_parsers.cc
+++ b/net/tools/transport_security_state_generator/input_file_parsers.cc
@@ -167,6 +167,12 @@ enum class CertificateParserState {
 }  // namespace
 
 bool ParseCertificatesFile(base::StringPiece certs_input, Pinsets* pinsets) {
+  if (certs_input.find("\r\n") != base::StringPiece::npos) {
+    LOG(ERROR) << "CRLF line-endings found in the pins file. All files must "
+                  "use LF (unix style) line-endings.";
+    return false;
+  }
+
   std::string line;
   CertificateParserState current_state = CertificateParserState::PRE_NAME;