Start tracking Document::detach for performance issues
Start tracking Document::detach for performance issues

Document::detach is expensive on real pages (e.g., 8ms when navigating
away from wikipedia cats on a high-end laptop).

Review URL: https://codereview.chromium.org/1351913003

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@202494 bbb929c8-8fbe-4397-9dbb-9b2b20218538

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk