Fill in descriptions on relevant blink_perf tests

PerformanceTests/Animation/balls-transitions.html

Index: PerformanceTests/Animation/balls-transitions.html
diff --git a/PerformanceTests/Animation/balls-transitions.html b/PerformanceTests/Animation/balls-transitions.html
index c9260b649894ab284e063ac9aa61ef03c483c078..6df69e4c070239f5b36444eecaaa18cb6b9046e9 100644
--- a/PerformanceTests/Animation/balls-transitions.html
+++ b/PerformanceTests/Animation/balls-transitions.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).',

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

"Measure performance of CSS Transitions animating 'left' and 'top' with
transition-property: 'left, top'."

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