Revert of Allow overriding GN build flags (patchset #2 id:20001 of https://codereview.chromium.org/1923333002/ )

Reason for revert:
Blocking the roll

Original issue's description:
> Allow overriding GN build flags
>
> In order to enable XFA from GN builds we need to be able to override
> pdf_enable_xfa. To do this a build_overrides/pdfium.gni file needs to be created
> in Chrome. To use that, we have to create a build_overrides/pdfium.gni file
> in PDFium that just uses the default values.
>
> BUG=chromium:62400
>
> Committed: https://pdfium.googlesource.com/pdfium/+/1ae572e7e35b52ce4897d1715c005a1b0f79526a

TBR=thakis@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=chromium:62400

Review-Url: https://codereview.chromium.org/1941563002
diff --git a/pdfium.gni b/pdfium.gni
new file mode 100644
index 0000000..b85ac74
--- /dev/null
+++ b/pdfium.gni
@@ -0,0 +1,23 @@
+# Copyright 2015 PDFium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+# This file contains PDFium-related build flags.
+
+declare_args() {
+  # On Android there's no system FreeType. On Windows and Mac, only a few
+  # methods are used from it.
+  pdfium_bundle_freetype = !is_linux
+
+  # Build PDFium either with or without v8 support.
+  pdf_enable_v8 = true
+
+  # Build PDFium either with or without XFA Forms support.
+  pdf_enable_xfa = false
+
+  # Build PDFium against skia (experimental) rather than agg.
+  pdf_use_skia = false
+
+  # Build PDFium standalone
+  pdf_is_standalone = false
+}