Add UMA for camera pixel formats and resolutions

These are measured the first time the capture process enumerates
devices. This can give insights into which pixel formats would be good
options for optimizations.

Tested with the unit tests, and compiling Chromium and checking
chrome://histograms

Bug: 1156144
Change-Id: Idb72a74822ac2e9206fadb37fe365fd85cb16a5a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2579510
Commit-Queue: Evan Shrubsole <eshr@google.com>
Reviewed-by: Markus Handell <handellm@google.com>
Reviewed-by: Weilun Shi <sweilun@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#836606}