ResolutionChangeDetector now does not update its internal state. There is no
impact because Reset() is always actively called.
So this change renames ResolutionChangeDetector to ResolutionTracker, and rename
the IsChanged() function into SetResolution(), which returns true if a
replacement happened. Internally it always records the latest DesktopSize.
Customers of this class can still use SetResolution() function to check whether
a DesktopSize change happened.
Bug: webrtc:8038
Change-Id: I6d25f3dd2d0567219a82b6688bf3e08560c8b0af
Reviewed-on: https://chromium-review.googlesource.com/587405
Reviewed-by: Jamie Walch <jamiewalch@chromium.org>
Commit-Queue: Zijie He <zijiehe@chromium.org>
Cr-Commit-Position: refs/heads/master@{#19184}
