It claimed (twice):

** Presubmit ERRORS **
Missing LGTM from an OWNER for these files:
    android_webview/browser/DEPS
    content/DEPS
    content/renderer/BUILD.gn
    content/renderer/DEPS
    content/renderer/browser_plugin/browser_plugin.cc
    content/renderer/child_frame_compositing_helper.cc
    content/renderer/child_frame_compositing_helper_unittest.cc
    content/renderer/gpu/render_widget_compositor.cc
    content/renderer/gpu/render_widget_compositor.h
    content/renderer/media/stream/webmediaplayer_ms.cc
    content/renderer/media/stream/webmediaplayer_ms.h
    content/renderer/pepper/pepper_compositor_host.cc
    content/renderer/pepper/pepper_plugin_instance_impl.cc
    content/renderer/render_frame_proxy.cc
    content/renderer/render_thread_impl.cc
    content/renderer/render_widget_fullscreen_pepper.cc
    content/renderer/renderer_blink_platform_impl.cc
    content/renderer/renderer_blink_platform_impl.h
    content/shell/test_runner/BUILD.gn
    content/shell/test_runner/test_plugin.cc
    content/test/DEPS
    content/test/test_blink_web_unit_test_support.cc
    content/test/test_blink_web_unit_test_support.h
    media/blink/BUILD.gn
    media/blink/DEPS
    media/blink/webmediaplayer_impl.cc
    media/blink/webmediaplayer_impl.h
    media/blink/webmediaplayer_impl_unittest.cc
    ui/snapshot/DEPS
    ui/views/mus/DEPS
Note that TBR does not apply to changes that affect OWNERS files.
Missing LGTM from an OWNER for these files:
    android_webview/browser/DEPS
    content/DEPS
    content/renderer/BUILD.gn
    content/renderer/DEPS
    content/renderer/browser_plugin/browser_plugin.cc
    content/renderer/child_frame_compositing_helper.cc
    content/renderer/child_frame_compositing_helper_unittest.cc
    content/renderer/gpu/render_widget_compositor.cc
    content/renderer/gpu/render_widget_compositor.h
    content/renderer/media/stream/webmediaplayer_ms.cc
    content/renderer/media/stream/webmediaplayer_ms.h
    content/renderer/pepper/pepper_compositor_host.cc
    content/renderer/pepper/pepper_plugin_instance_impl.cc
    content/renderer/render_frame_proxy.cc
    content/renderer/render_thread_impl.cc
    content/renderer/render_widget_fullscreen_pepper.cc
    content/renderer/renderer_blink_platform_impl.cc
    content/renderer/renderer_blink_platform_impl.h
    content/shell/test_runner/BUILD.gn
    content/shell/test_runner/test_plugin.cc
    content/test/DEPS
    content/test/test_blink_web_unit_test_support.cc
    content/test/test_blink_web_unit_test_support.h
    media/blink/BUILD.gn
    media/blink/DEPS
    media/blink/webmediaplayer_impl.cc
    media/blink/webmediaplayer_impl.h
    media/blink/webmediaplayer_impl_unittest.cc
    ui/snapshot/DEPS
    ui/views/mus/DEPS
Note that TBR does not apply to changes that affect OWNERS files.

I've got a TBR=jam line though, who is in src/OWNERS via src/ENG_REVIEW_OWNERS

TBR functionality is added by a Chromium-specific plugin.

Moved issue gerrit:8997 to now be  issue chromium:842797 .

This is working as intended. As noted in the output provided above:

"Note that TBR does not apply to changes that affect OWNERS files." 

Basically, our checks do not allow TBR changes that change OWNERS files. And I confirmed that the CL in question did change OWNERS files.