Maybe related to r386129? Maybe a timing issue?

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https://build.chromium.org/p/chromium.memory.fyi/builders/Linux%20Tests%20%28valgrind%29%283%29/builds/50556/

[ RUN      ] NativeDesktopMediaListTest.UpdateThumbnail
Xlib:  extension "RANDR" missing on display ":9".

GMOCK WARNING:
Uninteresting mock function call - returning directly.
    Function call: OnSourceRemoved(0x1cd9a540, 2)
NOTE: You can safely ignore the above warning unless this call should not happen.  Do not suppress it by blindly adding an EXPECT_CALL() if you don't mean to enforce the call.  See http://code.google.com/p/googlemock/wiki/CookBook#Knowing_When_to_Expect for details.

GMOCK WARNING:
Uninteresting mock function call - returning directly.
    Function call: OnSourceAdded(0x1cd9a540, 2)
NOTE: You can safely ignore the above warning unless this call should not happen.  Do not suppress it by blindly adding an EXPECT_CALL() if you don't mean to enforce the call.  See http://code.google.com/p/googlemock/wiki/CookBook#Knowing_When_to_Expect for details.
unknown file: Failure

Unexpected mock function call - returning directly.
    Function call: OnSourceThumbnailChanged(0x1cd9a540, 2)
Google Mock tried the following 1 expectation, but it didn't match:

../../chrome/browser/media/native_desktop_media_list_unittest.cc:478: EXPECT_CALL(observer_, OnSourceThumbnailChanged(model_.get(), 1))...
  Expected arg #1: is equal to 1
           Actual: 2
         Expected: to be called once
           Actual: called once - saturated and active
[  FAILED  ] NativeDesktopMediaListTest.UpdateThumbnail (1877 ms)
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https://build.chromium.org/p/chromium.memory.fyi/builders/Linux%20Tests%20%28valgrind%29%284%29/builds/48397/

[ RUN      ] NativeDesktopMediaListTest.AddNativeWindow
Xlib:  extension "RANDR" missing on display ":9".

GMOCK WARNING:
Uninteresting mock function call - returning directly.
    Function call: OnSourceThumbnailChanged(0x19932bf0, 3)
NOTE: You can safely ignore the above warning unless this call should not happen.  Do not suppress it by blindly adding an EXPECT_CALL() if you don't mean to enforce the call.  See http://code.google.com/p/googlemock/wiki/CookBook#Knowing_When_to_Expect for details.

GMOCK WARNING:
Uninteresting mock function call - returning directly.
    Function call: OnSourceRemoved(0x19932bf0, 2)
NOTE: You can safely ignore the above warning unless this call should not happen.  Do not suppress it by blindly adding an EXPECT_CALL() if you don't mean to enforce the call.  See http://code.google.com/p/googlemock/wiki/CookBook#Knowing_When_to_Expect for details.
unknown file: Failure

Unexpected mock function call - returning directly.
    Function call: OnSourceAdded(0x19932bf0, 2)
Google Mock tried the following 1 expectation, but it didn't match:

../../chrome/browser/media/native_desktop_media_list_unittest.cc:377: EXPECT_CALL(observer_, OnSourceAdded(model_.get(), index))...
  Expected arg #1: is equal to 3
           Actual: 2
         Expected: to be called once
           Actual: called once - saturated and active
[  FAILED  ] NativeDesktopMediaListTest.AddNativeWindow (1249 ms)
[ RUN      ] NativeDesktopMediaListTest.RemoveNativeWindow
Xlib:  extension "RANDR" missing on display ":9".
../../chrome/browser/media/native_desktop_media_list_unittest.cc:416: Failure
Mock function called more times than expected - returning directly.
    Function call: OnSourceRemoved(0x1eda8f50, 1)
         Expected: to be called once
           Actual: called twice - over-saturated and active

GMOCK WARNING:
Uninteresting mock function call - returning directly.
    Function call: OnSourceAdded(0x1eda8f50, 1)
NOTE: You can safely ignore the above warning unless this call should not happen.  Do not suppress it by blindly adding an EXPECT_CALL() if you don't mean to enforce the call.  See http://code.google.com/p/googlemock/wiki/CookBook#Knowing_When_to_Expect for details.
[  FAILED  ] NativeDesktopMediaListTest.RemoveNativeWindow (1531 ms)

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