[chromium] Update test expectations
https://bugs.webkit.org/show_bug.cgi?id=107587

Unreviewed. Mark these tests as slow on Win7 Debug:
platform/chromium/virtual/gpu/fast/hidpi/clip-text-in-hidpi.html
platform/chromium/virtual/gpu/fast/hidpi/device-scale-factor-paint.html
platform/chromium/virtual/gpu/fast/hidpi/focus-rings.html

* platform/chromium/TestExpectations:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@140471 268f45cc-cd09-0410-ab3c-d52691b4dbfc