Protobuf: Cherry-pick upstream r427.

third_party/protobuf/src/google/protobuf/compiler/command_line_interface.cc

Index: third_party/protobuf/src/google/protobuf/compiler/command_line_interface.cc
diff --git a/third_party/protobuf/src/google/protobuf/compiler/command_line_interface.cc b/third_party/protobuf/src/google/protobuf/compiler/command_line_interface.cc
index 1c76994bdcf8e555602ca99f3d8c75fd67994a3f..060a6127f27d0835c5ae1db54fce2893a345a5bf 100644
--- a/third_party/protobuf/src/google/protobuf/compiler/command_line_interface.cc
+++ b/third_party/protobuf/src/google/protobuf/compiler/command_line_interface.cc
@@ -890,7 +890,7 @@ bool CommandLineInterface::InterpretArgument(const string& name,
       string virtual_path;
       string disk_path;
 
-      int equals_pos = parts[i].find_first_of('=');
+      string::size_type equals_pos = parts[i].find_first_of('=');
       if (equals_pos == string::npos) {
         virtual_path = "";
         disk_path = parts[i];