Make context_lost test more of a stress test.

This change much more reliably catches the assertion failure in Issue 365904.

BUG=365904

Review URL: https://codereview.chromium.org/256433003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@265833 0039d316-1c4b-4281-b951-d872f2087c98
1 file changed