File Manager cleanup: Use CustomEvent type parameters.

Bug: 924733
Change-Id: I2a3120f6fb9164a700be4de9aaba321426f11130
Reviewed-on: https://chromium-review.googlesource.com/c/1469282
Auto-Submit: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#631516}
2 files changed