Only a couple of examples (I was hit by this, which is why I started looking):

https://luci-milo.appspot.com/buildbot/tryserver.chromium.win/win_chromium_rel_ng/449137
https://luci-milo.appspot.com/buildbot/tryserver.chromium.win/win_chromium_rel_ng/449121

Log excerpt:

[287/16603] ACTION //mojo/public/interfaces/bindings:bindings__generator(//build/toolchain/nacl:irt_x64)
FAILED: irt_x64/gen/mojo/public/interfaces/bindings/pipe_control_messages.mojom.cc irt_x64/gen/mojo/public/interfaces/bindings/pipe_control_messages.mojom.h irt_x64/gen/mojo/public/interfaces/bindings/pipe_control_messages.mojom.srcjar irt_x64/gen/mojo/public/interfaces/bindings/pipe_control_messages.mojom.js 
E:/b/depot_tools/python276_bin/python.exe ../../mojo/public/tools/bindings/mojom_bindings_generator.py --use_bundled_pylibs generate ../../mojo/public/interfaces/bindings/pipe_control_messages.mojom -d ../../ -I ../../ -o E:/b/c/b/win/src/out/Release/irt_x64/gen --bytecode_path E:/b/c/b/win/src/out/Release/irt_x64/gen/mojo/public/tools/bindings -g c++,javascript,java --depfile irt_x64/gen/mojo/public/interfaces/bindings/bindings__generator_pipe_control_messages.d --depfile_target irt_x64/gen/mojo/public/interfaces/bindings/pipe_control_messages.mojom.cc --typemap irt_x64/gen/mojo/public/interfaces/bindings/bindings__type_mappings --export_attribute MOJO_CPP_BINDINGS_EXPORT --export_header mojo/public/cpp/bindings/bindings_export.h --use_once_callback
Traceback (most recent call last):
  File "../../mojo/public/tools/bindings/mojom_bindings_generator.py", line 376, in <module>
    sys.exit(main())
  File "../../mojo/public/tools/bindings/mojom_bindings_generator.py", line 372, in main
    return args.func(args, remaining_args)
  File "../../mojo/public/tools/bindings/mojom_bindings_generator.py", line 276, in _Generate
    processor.ProcessFile(args, remaining_args, generator_modules, filename)
  File "../../mojo/public/tools/bindings/mojom_bindings_generator.py", line 169, in ProcessFile
    RelativePath(filename, args.depth))
  File "../../mojo/public/tools/bindings/mojom_bindings_generator.py", line 216, in _GenerateModule
    generator.GenerateFiles(filtered_args)
  File "E:\b\c\b\win\src\mojo\public\tools\bindings\generators\mojom_cpp_generator.py", line 395, in GenerateFiles
    self.Write(self._GenerateModuleHeader(),
  File "E:\b\c\b\win\src\mojo\public\tools\bindings\pylib\mojom\generate\template_expander.py", line 50, in GeneratorInternal
    return ApplyTemplate(args[0], path_to_template, parameters, **kwargs)
  File "E:\b\c\b\win\src\mojo\public\tools\bindings\pylib\mojom\generate\template_expander.py", line 42, in ApplyTemplate
    template = jinja_env.get_template(path_to_template)
  File "E:\b\c\b\win\src\third_party\jinja2\environment.py", line 812, in get_template
    return self._load_template(name, self.make_globals(globals))
  File "E:\b\c\b\win\src\third_party\jinja2\environment.py", line 786, in _load_template
    template = self.loader.load(self, name, globals)
  File "E:\b\c\b\win\src\third_party\jinja2\loaders.py", line 474, in load
    raise TemplateNotFound(name)
jinja2.exceptions.TemplateNotFound: module.h.tmpl


I don't know whether this was already found and fixed. My CL https://codereview.chromium.org/2894683003/ ran into this. I couldn't find any other recently bugs filed about this.

It looks like some of the Win builders might be running out of disk space. Some of the other failures of "compile (without patch)" on this tryserver look like corrupt .pdb files or similar. Not sure whether this could be caused by the same issue.

Marking P1 so this is at least looked at promptly, even if it's closed as WontFix.