chromium: add build flags and system libs

This is lifted from the Arch build recipe:
https://git.archlinux.org/svntogit/packages.git/tree/trunk/PKGBUILD?h=packages/chromium

using system libjpeg still doesn't work for some reason, otherwise the
build runs fine

pkgs/applications/networking/browsers/chromium/common.nix

···
     in attrs: concatStringsSep " " (attrValues (mapAttrs toFlag attrs));
 
   gnSystemLibraries = [
-    "ffmpeg" "flac" "harfbuzz-ng" "libwebp" "libxslt" "yasm" "snappy" # "libpng" "libjpeg"
+    "flac" "harfbuzz-ng" "libwebp" "libxslt" "yasm" "opus" "snappy" "libpng" "zlib"
+    # "libjpeg" # fails with multiple undefined references to chromium_jpeg_*
+    # "re2" # fails with linker errors
+    # "ffmpeg" # https://crbug.com/731766
   ];
 
   opusWithCustomModes = libopus.override {
···
     libpng libcap
     xdg_utils yasm minizip libwebp
     libusb1 re2 zlib
-    ffmpeg harfbuzz libxslt harfbuzz-icu libxml2
+    ffmpeg harfbuzz-icu libxslt libxml2
   ];
 
   # build paths and release info
···
       enable_hotwording = enableHotwording;
       enable_widevine = enableWideVine;
       use_cups = cupsSupport;
-    } // {
+
       treat_warnings_as_errors = false;
       is_clang = false;
+      clang_use_chrome_plugins = false;
+      remove_webcore_debug_symbols = true;
+      use_gtk3 = true;
+      enable_swiftshader = false;
+      fieldtrial_testing_like_official_build = true;
 
       # Google API keys, see:
       #   http://www.chromium.org/developers/how-tos/api-keys

pkgs/applications/networking/browsers/chromium/default.nix

···
 { newScope, stdenv, makeWrapper, makeDesktopItem, ed
-, glib, gtk2, gtk3, gnome2, gnome3, gsettings_desktop_schemas
+, glib, gtk3, gnome3, gsettings_desktop_schemas
 
 # package customization
 , channel ? "stable"
···
 
   inherit (stdenv.lib) versionAtLeast;
 
-  gtk = if (versionAtLeast version "59.0.0.0") then gtk3 else gtk2;
-  gnome = if (versionAtLeast version "59.0.0.0") then gnome3 else gnome2;
-
 in stdenv.mkDerivation {
   name = "chromium${suffix}-${version}";
   inherit version;
···
     makeWrapper ed
 
     # needed for GSETTINGS_SCHEMAS_PATH
-    gsettings_desktop_schemas glib gtk
+    gsettings_desktop_schemas glib gtk3
 
     # needed for XDG_ICON_DIRS
-    gnome.defaultIconTheme
+    gnome3.defaultIconTheme
   ];
 
   outputs = ["out" "sandbox"];