Important: WebGL should be hosting on an HTTPS site to request permição to use the microphone only once.
WebGL: Interacting with browser scripting:
http://docs.unity3d.com/Manual/webgl-interactingwithbrowserscripting.html http://docs.unity3d.com/ScriptReference/Application.ExternalCall.html
Speech recognition project for Google Chrome:
https://github.com/GoogleChrome/webplatform-samples/tree/master/webspeechdemo