Enable --serialize-toplevel by default.

R=vogelheim@chromium.org

Review URL: https://codereview.chromium.org/661343003

Cr-Commit-Position: refs/heads/master@{#24872}
git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24872 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/flag-definitions.h

@@ -462,7 +462,7 @@ DEFINE_BOOL(trace_deopt, false, "trace optimize function deoptimization")
 DEFINE_BOOL(trace_stub_failures, false,
             "trace deoptimization of generated code stubs")
 
-DEFINE_BOOL(serialize_toplevel, false, "enable caching of toplevel scripts")
+DEFINE_BOOL(serialize_toplevel, true, "enable caching of toplevel scripts")
 DEFINE_BOOL(trace_code_serializer, false, "print code serializer trace")
 
 // compiler.cc