Here's a cl with a failed build: https://codereview.webrtc.org/2511933002
The log from the patch error looks like:

Connecting to https://codereview.webrtc.org
Downloading patch from https://codereview.webrtc.org/2511933002/#ps1
      webrtc/api/android/jni/androidmediaencoder_jni.cc
      webrtc/api/webrtcsdp_unittest.cc
      webrtc/media/BUILD.gn
      webrtc/media/base/mediaconstants.cc
      webrtc/media/base/mediaconstants.h
  N   webrtc/media/engine/internalencoderfactory.cc
  N   webrtc/media/engine/internalencoderfactory.h
      webrtc/media/engine/payload_type_mapper.cc
      webrtc/media/engine/payload_type_mapper_unittest.cc
      webrtc/media/engine/videoencodersoftwarefallbackwrapper.cc
      webrtc/media/engine/videoencodersoftwarefallbackwrapper.h
      webrtc/media/engine/videoencodersoftwarefallbackwrapper_unittest.cc
      webrtc/media/engine/webrtcvideoengine2.cc
      webrtc/media/engine/webrtcvideoengine2.h
      webrtc/media/engine/webrtcvideoengine2_unittest.cc
      webrtc/video/BUILD.gn
      webrtc/video/end_to_end_tests.cc
      webrtc/video/video_quality_test.cc
      webrtc/video/video_send_stream_tests.cc
      webrtc/video_encoder.h
 D    webrtc/video/video_encoder.cc

Applying the patch from https://codereview.webrtc.org/2511933002/#ps1
webrtc/api/android/jni/androidmediaencoder_jni.cc
  Created missing directory webrtc/api/android/jni.
  Checking patch api/android/jni/androidmediaencoder_jni.cc...
  Applied patch api/android/jni/androidmediaencoder_jni.cc cleanly.

webrtc/api/webrtcsdp_unittest.cc
  Checking patch api/webrtcsdp_unittest.cc...
  Applied patch api/webrtcsdp_unittest.cc cleanly.

webrtc/media/BUILD.gn
  Created missing directory webrtc/media.
  Checking patch media/BUILD.gn...
  Applied patch media/BUILD.gn cleanly.

webrtc/media/base/mediaconstants.cc
  Created missing directory webrtc/media/base.
  Checking patch media/base/mediaconstants.cc...
  Applied patch media/base/mediaconstants.cc cleanly.

webrtc/media/base/mediaconstants.h
  Checking patch media/base/mediaconstants.h...
  Applied patch media/base/mediaconstants.h cleanly.

webrtc/media/engine/internalencoderfactory.cc
  Created missing directory webrtc/media/engine.
  Checking patch media/engine/internalencoderfactory.cc...
  Applied patch media/engine/internalencoderfactory.cc cleanly.

webrtc/media/engine/internalencoderfactory.h
  Checking patch media/engine/internalencoderfactory.h...
  Applied patch media/engine/internalencoderfactory.h cleanly.

webrtc/media/engine/payload_type_mapper.cc
  Checking patch media/engine/payload_type_mapper.cc...
  Applied patch media/engine/payload_type_mapper.cc cleanly.

webrtc/media/engine/payload_type_mapper_unittest.cc
  Checking patch media/engine/payload_type_mapper_unittest.cc...
  Applied patch media/engine/payload_type_mapper_unittest.cc cleanly.

webrtc/media/engine/videoencodersoftwarefallbackwrapper.cc
  Checking patch media/engine/videoencodersoftwarefallbackwrapper.cc...
  Applied patch media/engine/videoencodersoftwarefallbackwrapper.cc cleanly.

webrtc/media/engine/videoencodersoftwarefallbackwrapper.h
  Checking patch media/engine/videoencodersoftwarefallbackwrapper.h...
  Applied patch media/engine/videoencodersoftwarefallbackwrapper.h cleanly.

webrtc/media/engine/videoencodersoftwarefallbackwrapper_unittest.cc
  Checking patch media/engine/videoencodersoftwarefallbackwrapper_unittest.cc...
  Applied patch media/engine/videoencodersoftwarefallbackwrapper_unittest.cc cleanly.

webrtc/media/engine/webrtcvideoengine2.cc
  Checking patch media/engine/webrtcvideoengine2.cc...
  Applied patch media/engine/webrtcvideoengine2.cc cleanly.

webrtc/media/engine/webrtcvideoengine2.h
  Checking patch media/engine/webrtcvideoengine2.h...
  Applied patch media/engine/webrtcvideoengine2.h cleanly.

webrtc/media/engine/webrtcvideoengine2_unittest.cc
  Checking patch media/engine/webrtcvideoengine2_unittest.cc...
  Applied patch media/engine/webrtcvideoengine2_unittest.cc cleanly.

webrtc/video/BUILD.gn
  Created missing directory webrtc/video.
  Checking patch video/BUILD.gn...
  Applied patch video/BUILD.gn cleanly.

webrtc/video/end_to_end_tests.cc
  Checking patch video/end_to_end_tests.cc...
  Applied patch video/end_to_end_tests.cc cleanly.

webrtc/video/video_quality_test.cc
  Checking patch video/video_quality_test.cc...
  Applied patch video/video_quality_test.cc cleanly.

webrtc/video/video_send_stream_tests.cc
  Checking patch video/video_send_stream_tests.cc...
  Applied patch video/video_send_stream_tests.cc cleanly.

webrtc/video_encoder.h
  Checking patch video_encoder.h...
  Applied patch video_encoder.h cleanly.

Failed to apply patch for webrtc/video/video_encoder.cc:
While running git rm webrtc/video/video_encoder.cc;
  fatal: pathspec 'webrtc/video/video_encoder.cc' did not match any files


The problem is that the line:
            stdout.append(self._check_output_git(['rm', p.filename]))
at https://cs.chromium.org/chromium/tools/depot_tools/checkout.py?rcl=0&l=264 doesn't take into account the p.patchlevel when it's about to delete the file, which makes the path be incorrect. Adding support for that shouldn't be that hard.