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

android_webview/common/BUILD.gn

Index: android_webview/common/BUILD.gn
diff --git a/android_webview/common/BUILD.gn b/android_webview/common/BUILD.gn
index 4be51790174fed0d15fded6cd6fea3ec0e704362..3ef5f80a9318fa859beb71e8d968ef0085c8fdee 100644
--- a/android_webview/common/BUILD.gn
+++ b/android_webview/common/BUILD.gn
@@ -2,9 +2,12 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("//chrome/version.gni")
+import("//build/util/process_version.gni")
 
 process_version("version") {
+  sources = [
+    "//chrome/VERSION",
+  ]
   template_file = "aw_version_info_values.h.version"
   output = "$root_gen_dir/android_webview/common/aw_version_info_values.h"
 }