SharedFunctionInfo::GetSourceCodeHarmony uses whitespaces
between arguments. This CL adds whitespaces for JSFunction::ToString
for wrapped functions as well.

Bug: v8:7172
Change-Id: I8fde1842735aa35a427dfe5150a209f9cb640bf3
Reviewed-on: https://chromium-review.googlesource.com/832476Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50222}