Move Android version stamping from an exec_script -> build rule

build/util/BUILD.gn

Index: build/util/BUILD.gn
diff --git a/build/util/BUILD.gn b/build/util/BUILD.gn
index c18f0ce25b93d6cc928cdc7446ed84218f2cf1f1..29dd9439cadcb3bf4ce9171f5d9d07772550723d 100644
--- a/build/util/BUILD.gn
+++ b/build/util/BUILD.gn
@@ -26,3 +26,23 @@ action("webkit_version") {
     rebase_path(output_file, root_build_dir),
   ]
 }
+
+action("chrome_version_json") {
+  script = "version.py"
+  _chrome_version_path = "//chrome/VERSION"
+  inputs = [
+    _chrome_version_path,
+  ]
+  _output_file = "$root_gen_dir/CHROME_VERSION.json"
+  outputs = [
+    _output_file,
+  ]
+  args = [
+    "--file",
+    rebase_path(_chrome_version_path, root_build_dir),
+    "--template",
+    "{\"full-quoted\": \"\\\"@MAJOR@.@MINOR@.@BUILD@.@PATCH@\\\"\"}",
+    "--output",
+    rebase_path(_output_file, root_build_dir),
+  ]
+}