Add a command-line switch --enable-per-tile-painting.

webkit/glue/webpreferences.cc

Index: webkit/glue/webpreferences.cc
diff --git a/webkit/glue/webpreferences.cc b/webkit/glue/webpreferences.cc
index 5d36a3747a51ee9c2f22e71e83c1138d0f6bba60..cd6ec57240a577f8823cdbb4e5e9ac3b6aae0ccf 100644
--- a/webkit/glue/webpreferences.cc
+++ b/webkit/glue/webpreferences.cc
@@ -95,7 +95,8 @@ WebPreferences::WebPreferences()
       should_print_backgrounds(false),
       enable_scroll_animator(false),
       hixie76_websocket_protocol_enabled(false),
-      visual_word_movement_enabled(false) {
+      visual_word_movement_enabled(false),
+      per_tile_drawing_enabled(false) {
 }
 
 WebPreferences::~WebPreferences() {
@@ -328,5 +329,8 @@ void WebPreferences::Apply(WebView* web_view) const {
       hixie76_websocket_protocol_enabled);
   settings->setVisualWordMovementEnabled(visual_word_movement_enabled);
 
+  // Enable per-tile drawing if requested on the command line.
+  settings->setPerTileDrawingEnabled(per_tile_drawing_enabled);
+
   WebNetworkStateNotifier::setOnLine(is_online);
 }