Google Chrome	70.0.3524.2 (Official Build) canary (64-bit)
Firmware Version Google_Eve.9584.160.0

Steps to repro:
# Enable dictation via Settings > Manage Accessibility Settings
# Go to the Launcher search field 
# Press search + d to start navigation
# Start speaking test words, each in their own dictation session: apple, shortcut, water, candle
Expected: just that one spoken word is entered
Actual: it is repeated several times and extra characters are entered
Intermittent

This does not reproduce in other text fields such as the Omnibox or the text field in this bug

Does not reproduce on Google Chrome 69,0,3497.35 (Official Build) dev (64-bit)
Firmware Version Google_Lulu.6301.136.57

Please see videos demonstrating problem. 

On the first one, I was only able to reproduce the problem once: https://drive.google.com/file/d/1tVwO7UOWzO4MTHKzyvTmBR158GPThrVB/view

On the second try: I was able to reproduce it twice: https://drive.google.com/file/d/125-fKHZecbAXnUnrHT65zELHtbK8iC41/view

You'll notice a double earcon for start and stop. I think that's just recording the system audio + the sound being picked up by the microphone.