[perf-test] Add a benchmark for body.scrollTop

[perf-test] Add a benchmark for body.scrollTop
https://bugs.webkit.org/show_bug.cgi?id=86806

Reviewed by Ryosuke Niwa.

Currently Bindings/dom-attributes.html is just a collection of random
DOM attributes and methods. We should remove it and instead add more
reasonable micro benchmarks by classifying DOM binding call paths.

This patch adds a benchmark for body.scrollTop, which covers other
DOM attributes that return small integers.

(Note: Performance optimization for the benchmark will be coming soon.)

Test results in my Linux desktop:

RESULT Bindings: scroll-top= 209.410654239 runs/s
median= 211.64021164 runs/s, stdev= 4.09958741195 runs/s, min= 201.005025126 runs/s, max= 212.483399734 runs/s

RESULT Bindings: scroll-top= 195.651111157 runs/s
median= 196.319018405 runs/s, stdev= 1.77011627406 runs/s, min= 191.846522782 runs/s, max= 197.28729963 runs/s
RESULT Bindings: scroll-top= 200.004907612 runs/s
median= 201.511335013 runs/s, stdev= 3.27455403827 runs/s, min= 193.236714976 runs/s, max= 202.53164557 runs/s

RESULT Bindings: scroll-top= 209.582737512 runs/s
median= 210.803689065 runs/s, stdev= 3.16769655464 runs/s, min= 203.045685279 runs/s, max= 211.920529801 runs/s

RESULT Bindings: scroll-top= 199.924607687 runs/s
median= 201.13144338 runs/s, stdev= 3.11080503619 runs/s, min= 193.003618818 runs/s, max= 202.02020202 runs/s

* Bindings/scroll-top.html: Added.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@117547 268f45cc-cd09-0410-ab3c-d52691b4dbfc