Layout/floats.html should be runnable by run-perf-tests

Layout/floats.html should be runnable by run-perf-tests
https://bugs.webkit.org/show_bug.cgi?id=77051

Reviewed by Ryosuke Niwa.

I've split Layout/floats.html into multiple tests for each button in the original manual test.
Some tests take longer to run and I've changed the number of iterations, so that each tests finishes under 30s per run.

* DOM/resources/dom-perf.js:
* Layout/floats.html: Removed.
* Layout/floats_100_100.html: Added.
* Layout/floats_100_100_nested.html: Added.
* Layout/floats_20_100.html: Added.
* Layout/floats_20_100_nested.html: Added.
* Layout/floats_2_100.html: Added.
* Layout/floats_2_100_nested.html: Added.
* Layout/floats_50_100.html: Added.
* Layout/floats_50_100_nested.html: Added.
* Layout/resources/floats.css: Added.
(.container):
(.float):
(.big):
(.float-end):
* Layout/resources/floats.js: Added.
(.):
* Skipped:
* resources/runner.js:
(PerfTestRunner.resetRandomSeed):
(PerfTestRunner.random):
(Math.random):
    Moved the Math.random to runner.js to be used by all tests.
    Added resetRandomSeed to bring the randomizer back to initial seed.
    It is useful to get the same results at every run and minimize the
    differences between runs.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@110801 268f45cc-cd09-0410-ab3c-d52691b4dbfc