Passing negative values to AudioParam.exponentialRampToValueAtTime

Currently the spec says that an exception should be thrown if the value
passed to this function is negative, but this makes it impossible to use
this function when scheduling automation events for AudioParams that need
to have negative values, such as DynamicsCompressorNode.threshold.

I believe that this restriction must be lifted.  Currently WebKit/Blink do
not respect what the spec says here, but Gecko does.  Are there any
objections to me removing this restriction and lifting it inside Gecko as
well?

Thanks!
--
Ehsan
<http://ehsanakhgari.org/>