Add command line flags for compositor's default tile size and

webkit/glue/webpreferences.h

Index: webkit/glue/webpreferences.h
===================================================================
--- webkit/glue/webpreferences.h	(revision 137957)
+++ webkit/glue/webpreferences.h	(working copy)
@@ -121,6 +121,11 @@
   bool per_tile_painting_enabled;
   bool css_regions_enabled;
   bool css_shaders_enabled;
+  int default_tile_width;
+  int default_tile_height;
+  int max_untiled_layer_width;
+  int max_untiled_layer_height;
+
   // We try to keep the default values the same as the default values in
   // chrome, except for the cases where it would require lots of extra work for
   // the embedder to use the same default value.