Fill in descriptions on relevant blink_perf tests

PerformanceTests/Animation/balls-keyframe-animations.html

Index: PerformanceTests/Animation/balls-keyframe-animations.html
diff --git a/PerformanceTests/Animation/balls-keyframe-animations.html b/PerformanceTests/Animation/balls-keyframe-animations.html
index 0d3da1f89752476fd4fd15b7e1b2d2456dcd3f81..90812a952c924d1bfee388f03d9a5e7342fe258a 100644
--- a/PerformanceTests/Animation/balls-keyframe-animations.html
+++ b/PerformanceTests/Animation/balls-keyframe-animations.html
@@ -70,7 +70,11 @@ var animationDuration = 10;
 var particles = [];
 
 window.onload = function () {
-    PerfTestRunner.prepareToMeasureValuesAsync({done: onCompletedRun, unit: 'fps'});
+    PerfTestRunner.prepareToMeasureValuesAsync({
+        description: 'Measures performance of CSS keyframes animation (animating on left and top).',

[rjwright, 2014/10/15 03:37:12]

"Measure performance of CSS Animations animating 'left' and 'top'."

Again to avoid confusion about which API is being tested.

+        done: onCompletedRun,
+        unit: 'fps'
+    });
 
     generateStyleElement();