Disable flaky DevToolsBeforeUnloadTest.TestDevToolsOnDevTools on Win.

BUG=323847
TEST=browser_tests.exe
TBR=lushnikov
NOTRY=TRUE

Review URL: https://codereview.chromium.org/131973003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243950 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243950