Revert "Ensure no frames have been decoded for video context loss tests."

This reverts commit 822a9853.

Reason for revert: crbug.com/1098750

Original change's description:
> Ensure no frames have been decoded for video context loss tests.
> 
> Once we have a valid video frame back from the decoder, we assume the
> decoder is good and toss the encoded data we hold onto for fallback.
> 
> It's unclear to me how the current tests have ever worked. Since we
> only fire canplaythrough after 4 frames have been decoded.
> 
> The fix for this is to ensure we don't decode any frames before
> triggering the gpu crash. This is fine for the purpose of this test
> which is for testing the rendering and not decoding.
> 
> R=​kbr
> 
> Bug: 1082761
> Change-Id: I7e798ff219ded36582b1576919b6e5bf9541f5fb
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2258772
> Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
> Reviewed-by: Kenneth Russell <kbr@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#781665}

TBR=dalecurtis@chromium.org,kbr@chromium.org

Change-Id: I02d1798b3799971d24229d95150cc76113ff9575
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1082761
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2264254Reviewed-by: Behdad Bakhshinategh <behdadb@chromium.org>
Commit-Queue: Behdad Bakhshinategh <behdadb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#781854}

content/test/data/gpu/pixel_video_context_loss.html

@@ -68,12 +68,6 @@ function Main() {
     domAutomationController.send('ERROR');
   }, false);
 
-  // We set a poster and preload=metadata to ensure that no frames are decoded
-  // before the gpu crash -- otherwise the media pipeline can't guarantee that
-  // we'll fall over to the software decoder.
-  video.poster = 'single_face.jpg';
-  video.preload = 'metadata';
-
   // src needs to be set after listeners are added.
   video.src = QueryString.src;
 }