Enable serializing eagerly compiled inner functions.

R=jochen@chromium.org

Review URL: https://codereview.chromium.org/830143004

Cr-Commit-Position: refs/heads/master@{#25966}

src/flag-definitions.h

@@ -498,7 +498,7 @@ DEFINE_BOOL(trace_stub_failures, false,
             "trace deoptimization of generated code stubs")
 
 DEFINE_BOOL(serialize_toplevel, true, "enable caching of toplevel scripts")
-DEFINE_BOOL(serialize_inner, false, "enable caching of inner functions")
+DEFINE_BOOL(serialize_inner, true, "enable caching of inner functions")
 DEFINE_BOOL(trace_serializer, false, "print code serializer trace")
 
 // compiler.cc