Fix Media Remoting Connector stream ID message parsing.

chrome/browser/media/cast_remoting_connector_messaging.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/media/cast_remoting_connector_messaging.h"
 
 #include <stdio.h>
 
 #include <limits>
 
@@ skipping 32 matching lines @@
 
 // static
 int32_t CastRemotingConnectorMessaging::GetStreamIdFromStartedMessage(
     base::StringPiece message, base::StringPiece specifier) {
   auto start = message.find(specifier);
   if (start == std::string::npos)
     return -1;
   start += specifier.size();
   if (start + 1 >= message.size())
     return -1; // Must be at least one hex digit following the specifier.
+  const auto length = message.find(kMessageFieldSeparator, start) - start;
   int parsed_value;
-  if (!base::HexStringToInt(
-          message.substr(start, message.find(kMessageFieldSeparator, start)),
-          &parsed_value) ||
+  if (!base::HexStringToInt(message.substr(start, length), &parsed_value) ||
       parsed_value < 0 ||
       parsed_value > std::numeric_limits<int32_t>::max()) {
     return -1; // Non-hex digits, or outside valid range.
   }
   return static_cast<int32_t>(parsed_value);
 }