What's the perf penalty for the thread hop? If it's small it might not be worth the code complexity.

The code complexity is minimal. We'd only need to make sure the callers wouldn't choke on a synchronous return.

On some local runs the elapsed time with the thread hop is ~15ms and without is 0 (for the tiny image case). The delay varies with how busy the system is. It seems we run this at startup when the system is often very busy.

15 ms seems worth it. Thanks for measuring.

CL: https://codereview.chromium.org/2824883006/

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e4135c8d12a6554d16e3bf16a8b79bb6462aa7d8

commit e4135c8d12a6554d16e3bf16a8b79bb6462aa7d8
Author: bruthig <bruthig@chromium.org>
Date: Tue Apr 25 19:27:47 2017

[ash-md] Reduce thread hopping for cheap wallpaper color extraction.

Recent optimizations to the color_analysis::CalculateProminentColorOfBitmap()
has made it more expensive to perform color extraction asynchronously in some
cases. This change uses a simple image size heuristic to decide whether to
extract colors synchronously or asynchronously.

The optimizations made the 0-3 minute scale for the
'Ash.Wallpaper.TimeSpentExtractingColors' histogram overkill so it was replaced
with 'Ash.Wallpaper.ColorExtraction.Durations' one which uses a 0-10 second
scale.

This change also includes a new 'Ash.Wallpaper.ColorExtraction.UserDelay'
histogram that includes the thread switching delays incurred by asynchronous
calculations.

BUG=595010,  712714 
TEST=components_unittests --gtest_filter=*WallPaperColorCalculator*yncTest*

Review-Url: https://codereview.chromium.org/2824883006
Cr-Commit-Position: refs/heads/master@{#467075}

[modify] https://crrev.com/e4135c8d12a6554d16e3bf16a8b79bb6462aa7d8/components/wallpaper/wallpaper_color_calculator.cc
[modify] https://crrev.com/e4135c8d12a6554d16e3bf16a8b79bb6462aa7d8/components/wallpaper/wallpaper_color_calculator.h
[modify] https://crrev.com/e4135c8d12a6554d16e3bf16a8b79bb6462aa7d8/components/wallpaper/wallpaper_color_calculator_unittest.cc
[modify] https://crrev.com/e4135c8d12a6554d16e3bf16a8b79bb6462aa7d8/tools/metrics/histograms/histograms.xml

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e4135c8d12a6554d16e3bf16a8b79bb6462aa7d8

commit e4135c8d12a6554d16e3bf16a8b79bb6462aa7d8
Author: bruthig <bruthig@chromium.org>
Date: Tue Apr 25 19:27:47 2017

[ash-md] Reduce thread hopping for cheap wallpaper color extraction.

Recent optimizations to the color_analysis::CalculateProminentColorOfBitmap()
has made it more expensive to perform color extraction asynchronously in some
cases. This change uses a simple image size heuristic to decide whether to
extract colors synchronously or asynchronously.

The optimizations made the 0-3 minute scale for the
'Ash.Wallpaper.TimeSpentExtractingColors' histogram overkill so it was replaced
with 'Ash.Wallpaper.ColorExtraction.Durations' one which uses a 0-10 second
scale.

This change also includes a new 'Ash.Wallpaper.ColorExtraction.UserDelay'
histogram that includes the thread switching delays incurred by asynchronous
calculations.

BUG=595010,  712714 
TEST=components_unittests --gtest_filter=*WallPaperColorCalculator*yncTest*

Review-Url: https://codereview.chromium.org/2824883006
Cr-Commit-Position: refs/heads/master@{#467075}

[modify] https://crrev.com/e4135c8d12a6554d16e3bf16a8b79bb6462aa7d8/components/wallpaper/wallpaper_color_calculator.cc
[modify] https://crrev.com/e4135c8d12a6554d16e3bf16a8b79bb6462aa7d8/components/wallpaper/wallpaper_color_calculator.h
[modify] https://crrev.com/e4135c8d12a6554d16e3bf16a8b79bb6462aa7d8/components/wallpaper/wallpaper_color_calculator_unittest.cc
[modify] https://crrev.com/e4135c8d12a6554d16e3bf16a8b79bb6462aa7d8/tools/metrics/histograms/histograms.xml

Verified on veyron_minnie v 60.0.3084.0

Your change meets the bar and is auto-approved for M59. Please go ahead and merge the CL to branch 3071 manually. Please contact milestone owner if you have questions.
Owners: amineer@(Android), cmasso@(iOS), gkihumba@(ChromeOS), Abdul Syed@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b04dec51600619369fb66ae642960d5df26bdbcd

commit b04dec51600619369fb66ae642960d5df26bdbcd
Author: Ben Ruthig <bruthig@chromium.org>
Date: Mon May 01 16:20:26 2017

[ash-md] Reduce thread hopping for cheap wallpaper color extraction.

Recent optimizations to the color_analysis::CalculateProminentColorOfBitmap()
has made it more expensive to perform color extraction asynchronously in some
cases. This change uses a simple image size heuristic to decide whether to
extract colors synchronously or asynchronously.

The optimizations made the 0-3 minute scale for the
'Ash.Wallpaper.TimeSpentExtractingColors' histogram overkill so it was replaced
with 'Ash.Wallpaper.ColorExtraction.Durations' one which uses a 0-10 second
scale.

This change also includes a new 'Ash.Wallpaper.ColorExtraction.UserDelay'
histogram that includes the thread switching delays incurred by asynchronous
calculations.

BUG=595010,  712714 
TEST=components_unittests --gtest_filter=*WallPaperColorCalculator*yncTest*

Review-Url: https://codereview.chromium.org/2824883006
Cr-Commit-Position: refs/heads/master@{#467075}
(cherry picked from commit e4135c8d12a6554d16e3bf16a8b79bb6462aa7d8)

Review-Url: https://codereview.chromium.org/2849163002 .
Cr-Commit-Position: refs/branch-heads/3071@{#324}
Cr-Branched-From: a106f0abbf69dad349d4aaf4bcc4f5d376dd2377-refs/heads/master@{#464641}

[modify] https://crrev.com/b04dec51600619369fb66ae642960d5df26bdbcd/components/wallpaper/wallpaper_color_calculator.cc
[modify] https://crrev.com/b04dec51600619369fb66ae642960d5df26bdbcd/components/wallpaper/wallpaper_color_calculator.h
[modify] https://crrev.com/b04dec51600619369fb66ae642960d5df26bdbcd/components/wallpaper/wallpaper_color_calculator_unittest.cc
[modify] https://crrev.com/b04dec51600619369fb66ae642960d5df26bdbcd/tools/metrics/histograms/histograms.xml