websql: Switch blink::Platform::DatabaseOpenFile() to return base::File.

Bug: 925739
Change-Id: Ia2e1fbe637ecf6ad0a090bd3302cfea16d893e54
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1525447
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Auto-Submit: Victor Costan <pwnall@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641309}
8 files changed