Fill in descriptions on relevant blink_perf tests

PerformanceTests/Animation/balls-transition-40-properties.html

Index: PerformanceTests/Animation/balls-transition-40-properties.html
diff --git a/PerformanceTests/Animation/balls-transition-40-properties.html b/PerformanceTests/Animation/balls-transition-40-properties.html
index 904874511e48047a2753d9b19d7a3358e533e03b..ab023dc859fed5e88b36de29ad21aff7f060f0a2 100644
--- a/PerformanceTests/Animation/balls-transition-40-properties.html
+++ b/PerformanceTests/Animation/balls-transition-40-properties.html
@@ -70,7 +70,11 @@ var testRunning = true;
 var particles = [];
 
 window.onload = function () {
-    PerfTestRunner.prepareToMeasureValuesAsync({done: onCompletedRun, unit: 'fps'});
+    PerfTestRunner.prepareToMeasureValuesAsync({
+        description: 'Measures performance of CSS transition animation (animating on left and top, transition-property: [40 properties]).',
+        done: onCompletedRun,

[rjwright, 2014/10/15 03:37:13]

As balls-transition-10-properties.html

+        unit: 'fps'
+    });
 
     // Create the particles
     for (var i = 0; i < maxParticles; i++) {