Propagate is_official_build to version script.

chrome/version.gni

 # Copyright 2014 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.
 
 import("//build/config/chrome_build.gni")
 
 # Runs the version processing script over the given template file to produce
 # an output file. This is used for generating various forms of files that
 # incorporate the product name and version.
 #
@@ skipping 77 matching lines @@
     if (defined(invoker.template_file)) {
       inputs += [ invoker.template_file ]
     }
 
     outputs = [
       invoker.output,
     ]
 
     args = []
 
+    if (is_official_build) {
+      args += [ "--official" ]
+    }
+
     if (defined(invoker.sources)) {
       inputs += invoker.sources
       foreach(i, invoker.sources) {
         args += [
           "-f",
           rebase_path(i, root_build_dir),
         ]
       }
     }
 
@@ skipping 32 matching lines @@
       forward_variables_from(invoker, [ "visibility" ])
       sources = get_target_outputs(":$action_name")
       public_deps = [
         ":$action_name",
       ]
     }
   }
 }
 
 chrome_version_rc_template = "//chrome/app/chrome_version.rc.version"