Failure happens on 6 out of 200 most recent builds:
https://uberchromegw.corp.google.com/i/chromium.win/builders/Win7%20Tests%20%28dbg%29%281%29?numbuilds=200

Builds:
https://uberchromegw.corp.google.com/i/chromium.win/builders/Win7%20Tests%20%28dbg%29%281%29/builds/57517
https://uberchromegw.corp.google.com/i/chromium.win/builders/Win7%20Tests%20%28dbg%29%281%29/builds/57440
https://uberchromegw.corp.google.com/i/chromium.win/builders/Win7%20Tests%20%28dbg%29%281%29/builds/57385
https://uberchromegw.corp.google.com/i/chromium.win/builders/Win7%20Tests%20%28dbg%29%281%29/builds/57368
https://uberchromegw.corp.google.com/i/chromium.win/builders/Win7%20Tests%20%28dbg%29%281%29/builds/57365
https://uberchromegw.corp.google.com/i/chromium.win/builders/Win7%20Tests%20%28dbg%29%281%29/builds/57340


Log contents:
UserManagerBrowserTest.UserManagerTest (run #1):
[ RUN      ] UserManagerBrowserTest.UserManagerTest
[7116:5444:0221/145038.021:INFO:media_foundation_video_encode_accelerator_win.cc(329)] Windows versions earlier than 8 are not supported.
[7116:5444:0221/145038.022:INFO:media_foundation_video_encode_accelerator_win.cc(329)] Windows versions earlier than 8 are not supported.
[3712:2996:0221/145054.198:INFO:CONSOLE(1221)] "Running TestCase UserManagerBrowserTest.UserManagerTest", source: test_api.js (1221)

UserManagerBrowserTest.UserManagerTest (run #2):
[ RUN      ] UserManagerBrowserTest.UserManagerTest
[5604:3976:0221/145645.704:INFO:media_foundation_video_encode_accelerator_win.cc(329)] Windows versions earlier than 8 are not supported.
[5604:3976:0221/145645.705:INFO:media_foundation_video_encode_accelerator_win.cc(329)] Windows versions earlier than 8 are not supported.
[1120:6720:0221/145649.621:ERROR:render_process_impl.cc(207)] WebFrame LEAKED 1 TIMES
[5564:6856:0221/145658.502:INFO:CONSOLE(1221)] "Running TestCase UserManagerBrowserTest.UserManagerTest", source: test_api.js (1221)
[5564:6856:0221/145728.067:INFO:CONSOLE(125)] "Page load time: 9079 ms", source: polymer_browser_test_base.js (125)
[5564:6856:0221/145728.068:INFO:CONSOLE(127)] "Test run time: 29555 ms", source: polymer_browser_test_base.js (127)
[5564:6856:0221/145728.069:INFO:CONSOLE(129)] "Total time: 38634 ms", source: polymer_browser_test_base.js (129)
[5604:3976:0221/145728.119:WARNING:ipc_message_attachment_set.cc(49)] MessageAttachmentSet destroyed with unconsumed attachments: 0/1

UserManagerBrowserTest.UserManagerTest (run #3):
[ RUN      ] UserManagerBrowserTest.UserManagerTest
[6060:5496:0221/145810.755:INFO:media_foundation_video_encode_accelerator_win.cc(329)] Windows versions earlier than 8 are not supported.
[6060:5496:0221/145810.756:INFO:media_foundation_video_encode_accelerator_win.cc(329)] Windows versions earlier than 8 are not supported.
[7096:6372:0221/145814.834:ERROR:render_process_impl.cc(207)] WebFrame LEAKED 1 TIMES
[5308:3452:0221/145814.869:ERROR:process_win.cc(140)] Unable to terminate process: Access is denied. (0x5)
[5308:5880:0221/145821.941:INFO:CONSOLE(1221)] "Running TestCase UserManagerBrowserTest.UserManagerTest", source: test_api.js (1221)
[5308:5880:0221/145852.282:INFO:CONSOLE(125)] "Page load time: 7211 ms", source: polymer_browser_test_base.js (125)
[5308:5880:0221/145852.285:INFO:CONSOLE(127)] "Test run time: 30331 ms", source: polymer_browser_test_base.js (127)
[5308:5880:0221/145852.288:INFO:CONSOLE(129)] "Total time: 37542 ms", source: polymer_browser_test_base.js (129)

UserManagerBrowserTest.UserManagerTest (run #4):
[ RUN      ] UserManagerBrowserTest.UserManagerTest
[3304:5104:0221/145855.407:INFO:media_foundation_video_encode_accelerator_win.cc(329)] Windows versions earlier than 8 are not supported.
[3304:5104:0221/145855.410:INFO:media_foundation_video_encode_accelerator_win.cc(329)] Windows versions earlier than 8 are not supported.
[3104:4104:0221/145858.752:ERROR:render_process_impl.cc(207)] WebFrame LEAKED 1 TIMES
[4144:1320:0221/145858.830:ERROR:process_win.cc(140)] Unable to terminate process: Access is denied. (0x5)
[4144:380:0221/145909.413:INFO:CONSOLE(1221)] "Running TestCase UserManagerBrowserTest.UserManagerTest", source: test_api.js (1221)


Assigning to test author per git blame

Not sure what component to use.