Roll Linux reference build to official build 31.0.1650.34 (trunk r224845, branch r230433)

README

Index: README
===================================================================
--- README	(revision 230844)
+++ README	(working copy)
@@ -13,11 +13,19 @@
 
   1. Select a target revision number that is green on all platforms.
 
-  2. Run src/tools/update_reference_build.py from a tmp directory. For example:
+  2. Run src/tools/update_reference_build.py from a tmp directory. To update a
+     Chromium reference build use -r <revision> option, for Chrome official
+     builds use -b <build_number>. To update a specific platform use
+     -p <platform> option. For example:
 
      $ cd /tmp
+     # Update a Chromium revision, example -r 123456
      $ /path/to/tools/update_reference_build.py -r <revision>
 
+     # Update a Chrome build, example -p Linux -b 30.0.1599.33
+     $ /path/to/tools/update_reference_build.py -p <platform> -b <build_number>
+
+
   3. Move to reference_builds/reference_builds and prepare a changelist.
      For example: