Add smooth scrolling command line switch for test_shell.

webkit/tools/test_shell/test_shell_main.cc

Index: webkit/tools/test_shell/test_shell_main.cc
diff --git a/webkit/tools/test_shell/test_shell_main.cc b/webkit/tools/test_shell/test_shell_main.cc
index d6aba54268495cf8c1296454f8c66e1ad940480d..8ae071423fd8e5536d31f001412539529c6ddc02 100644
--- a/webkit/tools/test_shell/test_shell_main.cc
+++ b/webkit/tools/test_shell/test_shell_main.cc
@@ -35,6 +35,7 @@
 #include "webkit/extensions/v8/playback_extension.h"
 #include "webkit/extensions/v8/profiler_extension.h"
 #include "webkit/glue/webkit_glue.h"
+#include "webkit/glue/webpreferences.h"
 #include "webkit/glue/window_open_disposition.h"
 #include "webkit/tools/test_shell/simple_resource_loader_bridge.h"
 #include "webkit/tools/test_shell/test_shell.h"
@@ -201,6 +202,9 @@ int main(int argc, char* argv[]) {
   if (parsed_command_line.HasSwitch(test_shell::kAllowScriptsToCloseWindows))
     TestShell::SetAllowScriptsToCloseWindows();
 
+  if (parsed_command_line.HasSwitch(test_shell::kEnableSmoothScrolling))
+    TestShell::GetWebPreferences()->enable_scroll_animator = true;
+
   // Disable user themes for layout tests so pixel tests are consistent.
 #if defined(OS_WIN)
   TestShellWebTheme::Engine engine;