Add fontconfig instructions to install-chromeos-fonts.py.

Update the install-chromeos-fonts.py script to also describe
how to configure fontconfig to use the default rendering
settings that are used on Chrome OS devices.

BUG=687626

Review-Url: https://codereview.chromium.org/2680913005
Cr-Original-Commit-Position: refs/heads/master@{#449406}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 5ae8facd914c824fed5b03f8c1f6e4fba8e436f1

linux/install-chromeos-fonts.py

@@ -82,6 +82,36 @@ def main(args):
     for file in files:
       os.chmod(os.path.join(base, file), 0644)
 
+  print """\
+
+Chrome OS font rendering settings are specified using Fontconfig. If your
+system's configuration doesn't match Chrome OS's (which vary for different
+devices), fonts may be rendered with different subpixel rendering, subpixel
+positioning, or hinting settings. This may affect font metrics.
+
+Chrome OS's settings are stored in the media-libs/fontconfig package, which is
+at src/third_party/chromiumos-overlay/media-libs/fontconfig in a Chrome OS
+checkout. You can configure your system to match Chrome OS's defaults by
+creating or editing a ~/.fonts.conf file:
+
+<?xml version="1.0"?>
+<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
+<fontconfig>
+  <match target="font">
+    <edit name="antialias" mode="assign"><bool>true</bool></edit>
+    <edit name="autohint" mode="assign"><bool>true</bool></edit>
+    <edit name="hinting" mode="assign"><bool>true</bool></edit>
+    <edit name="hintstyle" mode="assign"><const>hintslight</const></edit>
+    <edit name="rgba" mode="assign"><const>rgb</const></edit>
+  </match>
+</fontconfig>
+
+To load additional per-font configs (and assuming you have Chrome OS checked
+out), add the following immediately before the "</fontconfig>" line:
+
+  <include ignore_missing="yes">/path/to/src/third_party/chromiumos-overlay/media-libs/fontconfig/files/local.conf</include>
+"""
+
   return 0
 
 if __name__ == '__main__':