perf 的时候，将最长链路标红

[ChunelFeng]

digraph CGraph { compound=true; p0x126f04550[label="nodeA [start 0.45ms, finish 1005.47ms, per_cost 1005.02ms]"]; p0x126f04550 -> p0x126f04710 [color=red]; p0x126f04550 -> p0x126f048d0 [color=red]; p0x126f04710[label="nodeB [start 1005.48ms, finish 3010.55ms, per_cost 2005.07ms]"]; p0x126f04710 -> p0x126f04a90 [color=red]; p0x126f048d0[label="nodeC [start 1005.49ms, finish 2006.61ms, per_cost 1001.12ms]"]; p0x126f048d0 -> p0x126f04a90 [color=red]; p0x126f04a90[label="nodeD [start 3010.55ms, finish 5014.86ms, per_cost 2004.31ms]"]; }