ISSUE-2 (callback-value): Callback time parameter needs definition [Request Animation Frame]

ISSUE-2 (callback-value): Callback time parameter needs definition [Request Animation Frame]

http://www.w3.org/2010/webperf/track/issues/2

Raised by: Cameron McCormack
On product: Request Animation Frame

We need to decide what the time parameter passed in to callbacks actually represents -- the time at which the "sample all animations" algorithm starts, the time of the next display refresh, or something else.