Fill in descriptions on relevant blink_perf tests

PerformanceTests/Parser/html5-full-render.html

Index: PerformanceTests/Parser/html5-full-render.html
diff --git a/PerformanceTests/Parser/html5-full-render.html b/PerformanceTests/Parser/html5-full-render.html
index bcd7272dfea1f68bc940ad7b9192b75460367345..e4e2f87ddd1cf6a41a42ba0b74cdf21214aa98b8 100644
--- a/PerformanceTests/Parser/html5-full-render.html
+++ b/PerformanceTests/Parser/html5-full-render.html
@@ -4,9 +4,13 @@
 <script>
 // Running from the onload callback just makes the UI nicer as it shows the logs before starting the test.
 window.onload = function() {
-    PerfTestRunner.measurePageLoadTime({path: "resources/html5.html",
-    chunkSize: 500000 }); // 6.09mb / 500k = approx 13 chunks (thus 13 forced layouts/style resolves).
-}
+    PerfTestRunner.measurePageLoadTime({
+        description: "Measures performance of a full HTML5 document load.",
+        path: "resources/html5.html",
+        // 6.09mb / 500k = approx 13 chunks (thus 13 forced layouts/style resolves).
+        chunkSize: 500000
+    });
+};
 
 </script>
 </body>