Add description for new scheduler performance benchmark.

tools/perf/test-info.json

 {
   "_description":"This file contains info about our performance test suites, used by the perf dashboard (http://chromeperf.appspot.com).",
   "blink_perf":{
     "description":"Runs all enabled benchmarks in third_party/WebKit/PerformanceTests/",
     "code":[
       "chrome/src/tools/perf/measurements/blink_perf.py",
       "third_party/WebKit/PerformanceTests/"
     ]
   },
   "browsermark": {
@@ skipping 162 matching lines @@
   },
   "robohornet_pro":{
     "description":"Milliseconds to complete the [RoboHornetPro demo by Microsoft](http://ie.microsoft.com/testdrive/performance/robohornetpro/)"
   },
   "peacekeeper":{
     "description":"Peacekeeper measures browser's performance by testing its JavaScript functionality.\n\nJavaScript is a widely used programming language used in the creation of modern websites to provide features such as animation, navigation,forms and other common requirements. By measuring a browser's ability to handle commonly used JavaScript functions Peacekeeper can evaluate its performance. Peacekeeper scores are measured in operations per second or rendered frames per second depending on the test. Final Score is computed by calculating geometric mean of individual tests scores. [Peacekeeper by Futuremark](http://peacekeeper.futuremark.com)",
     "code":[
       "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":[
       "chrome/src/tools/perf/benchmark/scirra.py"
     ]
   },
   "sizes":{
     "description":"Tracks binary sizes and number of static initializers.",
     "code":[
       "chrome/tools/build/scripts/slave/chromium/sizes.py"
@@ skipping 19 matching lines @@
     "description":"Measures warm startup time with a dirty profile.",
     "comment":"The same as startup.warm.blank_page, except for the user profile that's used. Set up in tools/build/scripts/master/factory/chromium_factory.py."
   },
   "sunspider":{
     "description":"Performance on the [SunSpider JavaScript benchmark](http://www.webkit.org/perf/sunspider/sunspider.html)"
   },
   "tab_switching.top_10":{
     "description":"This test records the MPArch.RWH_TabSwitchPaintDuration histogram, which is a measure of the time between when a tab was requested to be shown, and when first paint occurred. The script opens 10 pages in different tabs, waits for them to load, and then switches to each tab and records the metric. The pages were chosen from Alexa top ranking sites."
   }
 }