Files.app: Fix exception thrown by ContentProvider if getLatest is called with the type 'media|thumbnail'.
Previously there is assumption in ContentProvider#fetch that only one request is
called for one URL at the same time, and the next request is never called before
the previous request completes. But actually multiple requests can be called for
each meatadata type. ContentProvider handles 'media' and 'thumbnail' metadata
type, so if both metadata type is specified, it causes an exception in
ContentProvider.
BUG=446396
TEST=FileManagerJsTest.MetadataCache
Review URL: https://codereview.chromium.org/806853007
Cr-Commit-Position: refs/heads/master@{#310061}
3 files changed
