Google Chrome	69.0.3494.0 (Official Build) dev (64-bit)
Firmware Version	Google_Lulu.6301.136.57

Steps:
# Turn on dictation using Accessibility Settings
# Put focus anywhere that contains a text field such as the Omnibox
# Start dictation by clicking the icon or search + d
# Talk continuously for over 30 seconds (a deep breath before this step helps)
Expected: dictation receives text for as long as it is on
Actual: dictation stays on even after no longer receiving text

Though this bug reproduces in the case where it no longer recognizes my speech, I'm not able to reliably get it to stop recognizing text while I'm speaking. Therefore it might be hard to reproduce "in the wild."  

Example utterance:
testing testing testing testing testing testing testing testing testing testing testing testing testing testing testing testing testing testing testing testing testing testing testing testing testing testing testing testing testing testing testing testing testing testing
(I kept talking after this point but it was no longer being recorded.)