Fixed #809: show a dialog when web platform experimental feature is not enabled
Added copyright headers
Moved script tag to head
Make polymer builder happy
nits
spark-splitter: Add size attribute
set splitter size
Revert "set splitter size"

This reverts commit a7f185c5091537a77025c0a3327b01c79f769aa7.
nits
Merge pull request #816 from sunglim/size_splitter

spark-splitter: Add size attribute
Merge pull request #810 from dinhviethoa/809-web-platform-xp-feature

show a dialog when web platform experimental feature is not enabled