Gardening: http/tests/loading/dont-preload-non-img-srcset.html is slow
Gardening: http/tests/loading/dont-preload-non-img-srcset.html is slow

BUG=311484
TBR=jsbell

Review URL: https://codereview.chromium.org/43263002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@160544 bbb929c8-8fbe-4397-9dbb-9b2b20218538

primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs