Simplify image-loading-subpixel-clip.html.

[chromium-wpt-export-bot]

Verified that it still fails with [1] applied and [2] reverted.

This may help with deflaking WPT [3]

[1] https://chromium-review.googlesource.com/c/chromium/src/+/2111906
[2] https://chromium-review.googlesource.com/c/chromium/src/+/2092698
[3] #22364

TBR:szager@chromium.org

Change-Id: Ie668c43c4d03ea442c37075c0e80be5ba1481fff
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2115932
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Reviewed-by: Stefan Zager <szager@chromium.org>
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#752511}

[wpt-pr-bot]

The review process for this patch is being conducted in the Chromium project.

[KyleJu]

@chrishtr Looks like this test still times out on Firefox and Chrome. Would you mind taking a second look?

Test	Subtest	Results	Messages
/html/semantics/embedded-content/the-img-element/image-loading-subpixel-clip.html		PASS: 8/10, TIMEOUT: 2/10

[chrishtr]

Will try to repro now.

[stephenmcgruer]

If it helps, I can reproduce on a fresh checkout of WPT via:

$ git checkout chromium-export-bb6643e9d8
$ ./wpt run --log-mach-level=info --log-mach=- --verify --verify-log-full --channel=experimental chrome html/semantics/embedded-content/the-img-element/image-loading-subpixel-clip.html 
...
 1:29.90 INFO ## Unstable results ##

 1:29.90 INFO |                                         Test                                        | Subtest |            Results            | Messages |
 1:29.90 INFO |-------------------------------------------------------------------------------------|---------|-------------------------------|----------|
 1:29.90 INFO | `/html/semantics/embedded-content/the-img-element/image-loading-subpixel-clip.html` |         | **PASS: 6/10, TIMEOUT: 4/10** |          |

Looking at the test - does target.onload fire even if the target has already loaded (if that is possible) when that script executes?

EDIT: if you want to pass a specific chrome binary in, you can pass the --binary=/path/to/chrome flag to wpt run. Note that you still need to set the 'product' as chrome, e.g. it looks like:

./wpt run --binary=/path/to/chrome --log-mach-level=info --log-mach=- --verify --verify-log-full --channel=experimental chrome html/semantics/embedded-content/the-img-element/image-loading-subpixel-clip.html

[chrishtr]

@stephenmcgruer I think you figured it out thanks. I reproduced the flakiness locally and I think
fixed it by setting the src attribute after adding the onload handler. I'll make a Chromium patch
now.

[stephenmcgruer]

Glad to hear it. Admin-merging this so that the following patch can be successfully exported. Note that you can check on the stabiltity checks/etc before merging a patch Chromium side. After sending it out for review look for the wpt-pr-bot to comment on it saying its been uploaded to GH (should contain a link to the PR) :).