Change UMA logging to only log once for same kind of error

`FullScreenPowerPointHandler::FindEditorWindow()` was previously
recording `FullScreenFindEditorResult` UMA metrics on every frame. This
causes log spam, especially when the heuristic fails due to multiple
editors having the same title.

This CL caches the previous result in `previous_find_editor_result_` and
only records the metric when the result differs from the previous call.

Bug: chromium:409473386
Change-Id: I44500864c89dd7415327c91778086ecd667cdd15
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/458041
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Commit-Queue: Palak Agarwal <agpalak@google.com>
Cr-Commit-Position: refs/heads/main@{#47193}