[Accessibility] Account for flag default in Android animation histograms

The initial implementation of this histogram used 0 as the default
setting. This will incorrectly count cases where the flag is missing as
'animation disabled'. This CL fixes this by splitting the default case
into its own enum. In order to preserve correct data, the old histogram
is obsoleted and a new histogram is created.

Bug: 722548
Change-Id: I031ca38cf70ddc8b51c9a150f31e25a305b9fc7a
Reviewed-on: https://chromium-review.googlesource.com/c/1351273
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Yaron Friedman <yfriedman@chromium.org>
Commit-Queue: Stephen McGruer <smcgruer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611674}
5 files changed