[fsp] Pass proper data to Notify().

This patch passes proper data instead of fake one to Notify(). Also, child
changes are now passed as a scoped_ptr and a reference to avoid unnecessary
copies.

Note, that end to end browser tests will come once notifications are wired to
chrome.fileManagerPrivate.

TEST=Tested manually.
BUG=248427

Review URL: https://codereview.chromium.org/656393002

Cr-Commit-Position: refs/heads/master@{#300062}
9 files changed