Detected 12 new flakes for test/step "external/wpt/offscreen-canvas/the-offscreen-canvas/offscreencanvas.convert.to.blob.w.html". To see the actual flakes, please visit https://chromium-try-flakes.appspot.com/all_flake_occurrences?key=ahVzfmNocm9taXVtLXRyeS1mbGFrZXNyZAsSBUZsYWtlIllleHRlcm5hbC93cHQvb2Zmc2NyZWVuLWNhbnZhcy90aGUtb2Zmc2NyZWVuLWNhbnZhcy9vZmZzY3JlZW5jYW52YXMuY29udmVydC50by5ibG9iLncuaHRtbAw. This message was posted automatically by the chromium-try-flakes app.

Reporting to stale-flakes-reports@google.com to investigate why this issue is not being processed despite being in an appropriate queue for 7 days or more.

 Issue 813462  has been merged into this issue.

+cc foolip@ (owner of LayoutTests/external) for help: 
Is there a way to let the layout tests in external/wpt/ folders run with additional driver flags? 
I know that for the usual Layout Tests, we can easily put them in a separate folder and mark it in VirtualTestSuites. Can we do the same for wpt tests?

The reason why I ask this is that these convertToBlob tests must be run in an environment when --enable-threaded-compositing is enabled, as the idle tasks can
only be run with this flag. Otherwise the convertToBlob will be switching to enforce encoding mode after a long waiting time for the idle task to begin. Currently, the rest of toBlob Layout Tests are all running with a flag (see
https://cs.chromium.org/chromium/src/third_party/WebKit/LayoutTests/VirtualTestSuites?l=21).

Yes, you can use VirtualTests in the same way, most things are just like LayoutTests. But you can't change the flags for the "non-virtual" configuration so you'll have to manage the duplication of coverage, possibly by skipping tests that aren't meaningful to run.

Thanks foolip@. CL waiting to be reviewed: https://chromium-review.googlesource.com/c/chromium/src/+/964395

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4282c508e7618f5999450ddf2e0ece2bb2cf9138

commit 4282c508e7618f5999450ddf2e0ece2bb2cf9138
Author: xlai <xlai@chromium.org>
Date: Mon Mar 19 15:21:08 2018

Improve wpt testing on OffscreenCanvas convertToBlob

Same as canvas.toBlob(), the OffscreenCanvas.convertToBlob() are running on
idle tasks by default. When idle tasks do not begin for a long time, they force
encoding on the current thread. As idle tasks are not enabled on layout tests
unless "--enable-threaded-compositing" flag is turned on, we therefore do both
virtual and non-virtual tests to ensure complete test coverage of both
execution paths--idle-task mode and force-encoding mode. The non-virtual tests
need to be marked as [Slow] as the CanvasAsyncBlobCreator is waiting for the
idle tasks for a threshold time before switching to force-encoding mode.

Bug:  817091 
Change-Id: I2c7da9e27ee2d24e1a5e6ee1c36597b46f052aca
Reviewed-on: https://chromium-review.googlesource.com/964395
Reviewed-by: Justin Novosad <junov@chromium.org>
Commit-Queue: Olivia Lai <xlai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544036}
[modify] https://crrev.com/4282c508e7618f5999450ddf2e0ece2bb2cf9138/third_party/WebKit/LayoutTests/SlowTests
[modify] https://crrev.com/4282c508e7618f5999450ddf2e0ece2bb2cf9138/third_party/WebKit/LayoutTests/TestExpectations
[modify] https://crrev.com/4282c508e7618f5999450ddf2e0ece2bb2cf9138/third_party/WebKit/LayoutTests/VirtualTestSuites
[rename] https://crrev.com/4282c508e7618f5999450ddf2e0ece2bb2cf9138/third_party/WebKit/LayoutTests/external/wpt/offscreen-canvas/convert-to-blob/offscreencanvas.convert.to.blob.html
[rename] https://crrev.com/4282c508e7618f5999450ddf2e0ece2bb2cf9138/third_party/WebKit/LayoutTests/external/wpt/offscreen-canvas/convert-to-blob/offscreencanvas.convert.to.blob.w.html
[add] https://crrev.com/4282c508e7618f5999450ddf2e0ece2bb2cf9138/third_party/WebKit/LayoutTests/virtual/threaded/external/wpt/offscreen-canvas/convert-to-blob/README.txt

I've watched the Flakiness dashboard and note that both converttoblob WPT tests are all running fine in these past two days.