[PerformanceTests] tests have dependencies

[PerformanceTests] tests have dependencies
https://bugs.webkit.org/show_bug.cgi?id=77506

Reviewed by Hajime Morita.

PerformanceTests:

* resources/init.html: Added.

Tools:

Load an initialization page before each test after starting a DRT so that
warming up DRT won't affect the performance test results.

* Scripts/webkitpy/performance_tests/perftestsrunner.py:
(PerfTestsRunner):
(PerfTestsRunner.__init__):
(PerfTestsRunner._run_tests_set):
(PerfTestsRunner._run_single_test):
* Scripts/webkitpy/performance_tests/perftestsrunner_unittest.py:
(MainTest.TestDriver.run_test):
(test_initial_page_loaded):
(test_initial_page_loaded.run_test):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@106543 268f45cc-cd09-0410-ab3c-d52691b4dbfc