setResourceTimingBufferSize should not clear "resource timing buffer full flag" when the buffer has shrunk

[rniwa]

When setResourceTimingBufferSize is called to shrink the resource timing buffer size, it's inappropriate to clear "resource timing buffer full flag" since that would result in every new queuing of a resource timing performance entry to fire resourcetimingbufferfull event even though there was no space made available in the buffer in the last firing of the event.

[npm1]

Should setResourceTimingBufferSize fire a resourcetimingbufferfull event if the maxSize parameter is less than or equal to resource timing buffer current size? I see that Chrome currently fires resourcetimingbufferfull in this case (regardless of the flag) but that is not stated anywhere in the spec.

[npm1]

I checked that Firefox 58 does not fire the event in this case, and the spec does not prompt this, so I think I should just fix the Chrome behavior.

[igrigorik]

Resolved via #146.