Add description for new scheduler performance benchmark.

tools/perf/test-info.json

Index: tools/perf/test-info.json
diff --git a/tools/perf/test-info.json b/tools/perf/test-info.json
index ae5896fd3627f339c93964bc6b729b61780e9b3e..87a0f90e8d2aeb0e7bb0964c38c78607b62327f5 100644
--- a/tools/perf/test-info.json
+++ b/tools/perf/test-info.json
@@ -180,6 +180,9 @@
       "chrome/src/tools/perf/benchmark/peacekeeper.py"
     ]
   },
+  "scheduler.tough_scheduling_cases":{
+    "description":"This test measures rendering statistics while interacting with pages that have challenging scheduling properties. Mainly affected by changes to the compositor scheduler or the graphics pipeline."
+  },
   "scirra":{
     "description":"The Scirra WebGL performance test measures the number of 2D triangles represented onscreen when the animation reaches the 30 FPS threshold. [Scirra demos](https://www.scirra.com/)",
     "code":[