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

chromecast/base/BUILD.gn

Index: chromecast/base/BUILD.gn
diff --git a/chromecast/base/BUILD.gn b/chromecast/base/BUILD.gn
index f24bb2c590b56a8bd9f4e336ddf82cadba251ba3..a757d3b01072f7167f788d336eb120945cfe82b1 100644
--- a/chromecast/base/BUILD.gn
+++ b/chromecast/base/BUILD.gn
@@ -2,7 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("//chrome/version.gni")  # TODO layering violation!
+import("//build/util/process_version.gni")
 import("//chromecast/chromecast.gni")
 import("//testing/test.gni")
 
@@ -200,6 +200,9 @@ process_version("cast_version") {
   template_file = "version.h.in"
   output = "$target_gen_dir/version.h"
 
+  sources = [
+    "//chrome/VERSION",
+  ]
   extra_args = [
     "-e",
     "VERSION_FULL=\"%s.%s.%s.%s\"%(MAJOR,MINOR,BUILD,PATCH)",