Currently, G1 uses the G1GCPercent flag to determine what should be its target GC overhead. The flag is non-product. We recently made changes to the G1 flags to use existing ones where possible (see 6928059 for example). So G1 should instead observe the existing GCTimeRatio flag instead of introducing a new one.
This is straightforward to implement. I will remove the G1GCPercent parameter and use GCTimeRatio to define the desired GC overhead for G1.