Suspect r581735 (OOBE).

[21164/43343] ACTION //chrome/browser:resources_grit(//build/toolchain/linux:clang_x64)
FAILED: gen/chrome/resources_stamp.d.stamp gen/chrome/grit/browser_resources.h gen/chrome/browser_resources.pak gen/chrome/browser_resources.pak.info 
python ../../tools/grit/grit.py -i ../../chrome/browser/browser_resources.grd build -o gen/chrome --depdir . --depfile gen/chrome/resources_stamp.d --write-only-new=1 --depend-on-stamp -D _google_chrome -E CHROMIUM_BUILD=google_chrome -D chromeos -D scale_factors=2x -D toolkit_views -D use_aura -D use_nss_certs -D use_ozone -D enable_app_list=true -D enable_arcore=false -D enable_background_mode=false -D enable_background_contents=true -D enable_extensions=true -D enable_hangout_services_extension=true -D enable_plugins=true -D enable_print_preview=true -D enable_printing=true -D enable_service_discovery=true -D enable_vr=false -D mac_views_browser=false -D safe_browsing_mode=1 -D optimize_webui=true -D enable_hangout_services_extension -E additional_modules_list_file=gen/chrome/browser/internal/additional_modules_list.txt -E root_gen_dir=gen -f ../../tools/gritsettings/resource_ids --assert-file-list=obj/chrome/browser/resources_expected_outputs.txt
Error processing node <?xml version="1.0" encoding="UTF-8"?>
<structure file="resources\chromeos\login\custom_elements_oobe.html" flattenhtml="true" name="IDR_CUSTOM_ELEMENTS_OOBE_HTML" type="chrome_html" />
Traceback (most recent call last):
  File "../../tools/grit/grit.py", line 15, in <module>
    grit.grit_runner.Main(sys.argv[1:])
  File "/b/c/b/Google_Chrome_ChromeOS/src/tools/grit/grit/grit_runner.py", line 249, in Main
    toolobject.Run(options, args[1:])
  File "/b/c/b/Google_Chrome_ChromeOS/src/tools/grit/grit/tool/build.py", line 249, in Run
    self.res.RunGatherers()
  File "/b/c/b/Google_Chrome_ChromeOS/src/tools/grit/grit/node/misc.py", line 651, in RunGatherers
    node.RunPreSubstitutionGatherer(debug=debug)
  File "/b/c/b/Google_Chrome_ChromeOS/src/tools/grit/grit/node/structure.py", line 224, in RunPreSubstitutionGatherer
    self.gatherer.Parse()
  File "/b/c/b/Google_Chrome_ChromeOS/src/tools/grit/grit/gather/chrome_html.py", line 358, in Parse
    filename_expansion_function=self.filename_expansion_function)
  File "/b/c/b/Google_Chrome_ChromeOS/src/tools/grit/grit/format/html_inline.py", line 533, in InlineToString
    filename_expansion_function=filename_expansion_function).inlined_data
  File "/b/c/b/Google_Chrome_ChromeOS/src/tools/grit/grit/format/html_inline.py", line 475, in DoInline
    flat_text = _INCLUDE_RE.sub(InlineIncludeFiles, flat_text)
  File "/b/c/b/Google_Chrome_ChromeOS/src/tools/grit/grit/format/html_inline.py", line 391, in InlineIncludeFiles
    return InlineFileContents(src_match, '%s')
  File "/b/c/b/Google_Chrome_ChromeOS/src/tools/grit/grit/format/html_inline.py", line 380, in InlineFileContents
    filename_expansion_function=filename_expansion_function)
  File "/b/c/b/Google_Chrome_ChromeOS/src/tools/grit/grit/format/html_inline.py", line 501, in DoInline
    flat_text = _SRC_RE.sub(SrcReplace, flat_text)
  File "/b/c/b/Google_Chrome_ChromeOS/src/tools/grit/grit/format/html_inline.py", line 288, in SrcReplace
    filename_expansion_function=filename_expansion_function)
  File "/b/c/b/Google_Chrome_ChromeOS/src/tools/grit/grit/format/html_inline.py", line 153, in SrcInlineAsDataURL
    inlined_files, names_only)
  File "/b/c/b/Google_Chrome_ChromeOS/src/tools/grit/grit/format/html_inline.py", line 122, in ConvertFileToDataURL
    'cannot be stored in a data url.' % filename)
Exception: ../../../internal/resources/chromeos/animations/oobe-welcome/laptop_G_intro.webm is of an an unknown type and cannot be stored in a data url.

Looks like this was already reverted a few minutes ago by alemate@: r581737.