gn: Generalize process_version() and move it to build/util

chrome/app/version_assembly/BUILD.gn

 # Copyright 2015 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/win/manifest.gni")
+import("//build/util/process_version.gni")
 import("//build/util/version.gni")
-import("//chrome/version.gni")
 
 version_assembly_output_file = "$target_gen_dir/version_assembly.manifest"
 
 # Generates a manifest file with the current build's version information.
 process_version("chrome_exe_version_manifest") {
   visibility = [ ":*" ]
   template_file = "chrome_exe_manifest.template"
+  sources = [
+    "//chrome/VERSION",
+  ]
   output = version_assembly_output_file
 }
 
 # Generates the manifest for chrome.exe. This is the normal manifest stuff plus
 # the version information.
 windows_manifest("chrome_exe_manifest") {
   sources = [
     as_invoker_manifest,
     common_controls_manifest,
     default_compatibility_manifest,
     version_assembly_output_file,
   ]
 
   type = "exe"
 
   deps = [
     ":chrome_exe_version_manifest",
   ]
 }
 
 # Generates the manifest for the version assembly, which is the versioned
 # directory where Chrome finds chrome.dll.
 process_version("version_assembly_manifest") {
   template_file = "version_assembly_manifest.template"
+  sources = [
+    "//chrome/VERSION",
+  ]
   output = "$root_build_dir/$chrome_version_full.manifest"
   process_only = true
 }