WebMediaPlayerMSCompositor: Fix excessive canvas cache reset

PaintCanvasVideoRenderer, for complicated reasons, maintains a cached
texture resulting from an YUV to RGB conversion. The goal of the cache
is not to avoid repeated YUV to RGB conversions, but to avoid repeated
allocation and freeing of the RGB texture every frame.

WebMediaPlayerMSCompositor::CheckForFrameChanges resets this cache every
time it gets a new frame, which makes the cache in
PaintCanvasVideoRenderer useless.

Change WebMediaPlayerMSCompositor::CheckForFrameChanges to only reset
the cache when the frame size changes.

Bug: 1235686
Change-Id: If8a6746fdc6828b9852653631d0de72777877b9c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3089355
Reviewed-by: Guido Urdaneta <[email protected]>
Reviewed-by: Dale Curtis <[email protected]>
Commit-Queue: ccameron <[email protected]>
Cr-Commit-Position: refs/heads/master@{#911727}

Author: ccameron-chromium

third_party/blink/renderer/modules/mediastream/webmediaplayer_ms_compositor.cc

@@ -708,10 +708,10 @@ void WebMediaPlayerMSCompositor::CheckForFrameChanges(
     PostCrossThreadTask(
         *main_task_runner_, FROM_HERE,
         CrossThreadBindOnce(&WebMediaPlayerMS::TriggerResize, player_));
+    PostCrossThreadTask(
+        *main_task_runner_, FROM_HERE,
+        CrossThreadBindOnce(&WebMediaPlayerMS::ResetCanvasCache, player_));
   }
-  PostCrossThreadTask(
-      *main_task_runner_, FROM_HERE,
-      CrossThreadBindOnce(&WebMediaPlayerMS::ResetCanvasCache, player_));
 }
 
 void WebMediaPlayerMSCompositor::StartRenderingInternal() {