UserTimingL3 uses returned value for feature detection. If measure and mark API returns null, the APIs are L2 API; If the APIs return an entry, the APIs are L3 API.

However, in the current implementation, when L3 API is enabled, the APIs do not always return the created entry.
 

UserTimingL3 uses returned value for feature detection. If measure and mark API returns null, the APIs are L2 API; If the APIs return an entry, the APIs are L3 API.

However, in the current implementation, when L3 API is disabled, the APIs do not always return the null.

Use case 1:
Repro steps (when CustomUserTiming is disabled):
1. Open console
2. performance.mark("name")
 
Expected:
return undefined
 
Actual:
return PerformanceMark entry
 

UserTimingL3 uses returned value for feature detection. If measure and mark API returns null, the APIs are L2 API; If the APIs return an entry, the APIs are L3 API.

However, in the current implementation, when L3 API is disabled, the APIs do not always return the null.

Use case 1:
Repro steps (when CustomUserTiming is disabled):
1. Open console
2. performance.mark("name")
 
Expected:
return undefined
 
Actual:
return PerformanceMark entry

Use case 2:
Repro steps (when CustomUserTiming is disabled):
1. Open console
2. performance.measure("name")
 
Expected:
return undefined
 
Actual:
return PerformanceMeasure entry