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* Add a validator that removes properties that are not the right type.
* Add double, time, and timedelta types in the document metadata mojo
  structure.
* Use the new mojo types in document metadata extractor.

Downstream clank will not be able to read fields parsed into the new
type, but will just skip over them. We should consider updating support
there.
http://cs/clank/java/src/com/google/android/apps/chrome/icing/AppIndexingReporterInternal.java?l=133

Bug: 1044250
Change-Id: Icfd7f0db74abf7bd1261b30dc416c94a7a23b4c0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2062907Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Becca Hughes <beccahughes@chromium.org>
Commit-Queue: Sam Bowen <sgbowen@google.com>
Cr-Commit-Position: refs/heads/master@{#748357}