Rename source_prereqs to inputs in the GN build.

build/util/BUILD.gn

 # Copyright (c) 2013 The Chromium 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 target generates a "last_change.h" header file in the generated files
 # directory that contains a define of the last revision of the source tree
 # of the form:
 #  #define LAST_CHANGE "123456"
 #
 # The version is a string rather than an integer for extra flexibility (for
 # example, we may require git hashes in the future).
 #
 # All you need to do is depend on this target, and then from your source code:
 #  #include "build/util/last_change.h"
 action("last_change") {
   script = "lastchange.py"
 
   # Rerun the script any time this file changes.
-  source_prereqs = [ "//build/util/LASTCHANGE" ]
+  inputs = [ "//build/util/LASTCHANGE" ]
 
   output_header = "$target_gen_dir/last_change.h"
   outputs = [ output_header ]
 
   build_relative_src = rebase_path("//", root_build_dir)
   build_relative_outputs = rebase_path(output_header, root_build_dir)
 
   args = [
     "--source-dir=$build_relative_src",
     "--header=$build_relative_outputs",
     "--version-macro=LAST_CHANGE",
   ]
 }
 
 action("webkit_version") {
   script = "version.py"
 
   lastchange_file = "LASTCHANGE.blink"
   # TODO(brettw) move from content to this directory.
   template_file = "//content/webkit_version.h.in"
-  source_prereqs = [ lastchange_file, template_file ]
+  inputs = [ lastchange_file, template_file ]
 
   output_file = "$root_gen_dir/webkit_version.h"
   outputs = [ output_file ]
 
   args = [
     "-f", rebase_path(lastchange_file, root_build_dir),
     rebase_path(template_file, root_build_dir),
     rebase_path(output_file, root_build_dir),
   ]
 }