docs: Change "ChromeOS" to "Chrome OS".

tools/gn/docs/reference.md

 # GN Reference
 
 *This page is automatically generated from* `gn help --markdown all`.
 
 ## **\--args**: Specifies build arguments overrides.
 
 ```
   See "gn help buildargs" for an overview of how build arguments work.
 
   Most operations take a build directory. The build arguments are taken from
@@ skipping 3875 matching lines @@
   primary object(s) of the build. It will match the OS of the default
   toolchain.
 
   In many cases, this is the same as "host_os", but in the case of
   cross-compiles, it may be different. This variable differs from "current_os"
   in that it can be referenced from inside any toolchain and will always return
   the initial value.
 
   This should be set to the most specific value possible. So, "android" or
   "chromeos" should be used instead of "linux" where applicable, even though
-  Android and ChromeOS are both Linux variants. This can mean that one needs to
+  Android and Chrome OS are both Linux variants. This can mean that one needs to
   write
 
       if (target_os == "android" || target_os == "linux") {
           # ...
       }
 
   and so forth.
 
   This value is not used internally by GN for any purpose, so it may be set to
   whatever value is needed for the build. GN defaults this value to the empty
@@ skipping 2758 matching lines @@
 **  \--root**: Explicitly specify source root.
 **  \--runtime-deps-list-file**: Save runtime dependencies for targets in file.
 **  \--script-executable**: Set the executable used to execute scripts.
 **  \--threads**: Specify number of worker threads.
 **  \--time**: Outputs a summary of how long everything took.
 **  \--tracelog**: Writes a Chrome-compatible trace log to the given file.
 **  -v**: Verbose logging.
 **  \--version**: Prints the GN version number and exits.
 
 ```