Should be ignored or correct expectation added. Can be seen when running with --single-process-tests or even just a --gtest_filter=. I reproduced on Android. 

35.681s run_tests_on_device(034b53ed215ca293)  Uninteresting mock function call - returning directly.
I   35.681s run_tests_on_device(034b53ed215ca293)      Function call: ReturnMixer(0xb4cfdbc0)
I   35.681s run_tests_on_device(034b53ed215ca293)  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.
I   35.681s run_tests_on_device(034b53ed215ca293)  
I   35.681s run_tests_on_device(034b53ed215ca293)  GMOCK WARNING:
I   35.681s run_tests_on_device(034b53ed215ca293)  Uninteresting mock function call - returning directly.
I   35.681s run_tests_on_device(034b53ed215ca293)      Function call: ReturnMixer(0xb4cfdbc0)
I   35.681s run_tests_on_device(034b53ed215ca293)  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.
I   35.681s run_tests_on_device(034b53ed215ca293)  
I   35.681s run_tests_on_device(034b53ed215ca293)  GMOCK WARNING:
I   35.681s run_tests_on_device(034b53ed215ca293)  Uninteresting mock function call - returning directly.
I   35.681s run_tests_on_device(034b53ed215ca293)      Function call: ReturnMixer(0xb4cfdbc0)
I   35.682s run_tests_on_device(034b53ed215ca293)  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.
I   35.682s run_tests_on_device(034b53ed215ca293)  
I   35.682s run_tests_on_device(034b53ed215ca293)  GMOCK WARNING:
I   35.682s run_tests_on_device(034b53ed215ca293)  Uninteresting mock function call - returning directly.
I   35.682s run_tests_on_device(034b53ed215ca293)      Function call: ReturnMixer(0xb4cfdbc0)
I   35.682s run_tests_on_device(034b53ed215ca293)  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.
I   35.682s run_tests_on_device(034b53ed215ca293)  
I   35.682s run_tests_on_device(034b53ed215ca293)  GMOCK WARNING:
I   35.682s run_tests_on_device(034b53ed215ca293)  Uninteresting mock function call - returning directly.
I   35.682s run_tests_on_device(034b53ed215ca293)      Function call: ReturnMixer(0xb4cfdbc0)
I   35.682s run_tests_on_device(034b53ed215ca293)  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.
I   35.682s run_tests_on_device(034b53ed215ca293)  
I   35.682s run_tests_on_device(034b53ed215ca293)  GMOCK WARNING:
I   35.682s run_tests_on_device(034b53ed215ca293)  Uninteresting mock function call - returning directly.