https://bugs.webkit.org/show_bug.cgi?id=121361

Reviewed by Filip Pizlo.

Add a DOM benchmark based on TodoMVC for vanilla JS, Ember.js, Backbone.js, and jQuery.
We'll add more frameworks and demo apps as we go.

* DoYouEvenBench: Added.
* DoYouEvenBench/benchmark.html: Added.
* DoYouEvenBench/benchmark.js: Added.
(SimplePromise): 
(SimplePromise.prototype.then):
(SimplePromise.prototype.resolve.else):
(SimplePromise.prototype.resolve):
(BenchmarkRunner.suite):
(BenchmarkRunner.waitForElement.resolveIfReady):
(BenchmarkRunner.waitForElement):
(BenchmarkRunner._removeFrame):
(BenchmarkRunner._appendFrame):
(BenchmarkRunner._waitAndWarmUp.Fibonacci):
(BenchmarkRunner._testName):
(BenchmarkRunner._testItemId):
(BenchmarkRunner.listSuites.button.onclick):
(BenchmarkRunner.listSuites.callNextStep):
(BenchmarkRunner.listSuites):
(BenchmarkState):
(BenchmarkState.prototype.currentSuite):
(BenchmarkState.prototype.currentTest):
(BenchmarkState.prototype.next):
(Benchm...