Rename source_prereqs to inputs in the GN build.

build/util/BUILD.gn

Index: build/util/BUILD.gn
diff --git a/build/util/BUILD.gn b/build/util/BUILD.gn
index 910900817365e2a173b7d678946803c5a9b516e9..e8f21cfcf6b1be1b4b7b1a0fca30015ae8ae58a2 100644
--- a/build/util/BUILD.gn
+++ b/build/util/BUILD.gn
@@ -16,7 +16,7 @@ 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 ]
@@ -37,7 +37,7 @@ action("webkit_version") {
   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 ]