Fix for decoder fallback metric

check to see if decoder name is not the same when setting fallback

Bug: 1027783
Change-Id: I7a8e9b6eb3b15c2d1f3a702474d35cf0e094c123
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1931648Reviewed-by: Dan Sanders <sandersd@chromium.org>
Commit-Queue: Ted Meyer <tmathmeyer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#718918}

media/mojo/services/media_metrics_provider.cc

@@ -199,7 +199,8 @@ void MediaMetricsProvider::SetHaveEnough() {
 
 void MediaMetricsProvider::SetVideoPipelineInfo(
     const PipelineDecoderInfo& info) {
-  if (!uma_info_.video_pipeline_info.decoder_name.empty())
+  auto old_name = uma_info_.video_pipeline_info.decoder_name;
+  if (!old_name.empty() && old_name != info.decoder_name)
     uma_info_.video_decoder_changed = true;
   uma_info_.video_pipeline_info = info;
 }