Build page with the recipe change run against the src-side change: https://ci.chromium.org/swarming/task/3ee16ec57b242e10?server=chromium-swarm.appspot.com

https://chromium-review.googlesource.com/c/chromium/tools/build/+/1147309#message-dba49cee4fd86b2b83124db5b06861c89ceabfe0

The line that was commented on was some debugging code I had to check the value of step_text, a previous line is modifying the step_text attribute.

oops, my fault

The step text is present in annotations
https://logs.chromium.org/logs/chromium/led/gbeaty_google.com/eddc62a67a4382d260449d2e940599dd251361e85cd33851bbec3b279a6d3e3b/+/stdout
but not in parsed annotation.proto
https://chromium-swarm.appspot.com/task?id=3ee16ec57b242e10&refresh=10&show_raw=1&wide_logs=true

the problem must be somewhere at the kitchen level, maybe in annotee

correction: step_text in https://logs.chromium.org/logs/chromium/led/gbeaty_google.com/eddc62a67a4382d260449d2e940599dd251361e85cd33851bbec3b279a6d3e3b/+/stdout
is step log. There is no @@@STEP_TEXT@GN Args@@@

the problem is at the recipe engine level. I don't see anything wrong with 
https://chromium-review.googlesource.com/c/chromium/tools/build/+/1147309/2/scripts/slave/recipe_modules/chromium/api.py#1070

Robbie, WDYT?

There's a new line before GN Args, so you won't find that string. 

In the stdout for the step (https://logs.chromium.org/logs/chromium/led/gbeaty_google.com/eddc62a67a4382d260449d2e940599dd251361e85cd33851bbec3b279a6d3e3b/+/steps/generate_build_files__with_patch_/0/stdout) there is a step text annotation:

@@@STEP_TEXT@
GN args:
dcheck_always_on = true
ffmpeg_branding = "Chrome"
goma_dir = "/b/swarming/w/ir/cache/goma/client"
is_component_build = false
is_debug = false
proprietary_codecs = true
strip_absolute_paths_from_debug_symbols = true
symbol_level = 0
use_goma = true
@@@

that's the bug :). Recipe engine should probably be converting newlines to <br>. As it is, none of those lines match the per-line annotation regex. For now I would recommend doing .replace('\n', '<br>')

Thanks, will make the change