Get rid of unnecessary layouts on body elements with quirky children

RenderBlockFlow::marginBeforeEstimateForChild() was checking the wrong
margin when detecting quirky children. The performance test added by
this patch times out without the change in this CL - obviously a
pathological case!

BUG=

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=169269

Review URL: https://codereview.chromium.org/190913003

git-svn-id: svn://svn.chromium.org/blink/trunk@169790 bbb929c8-8fbe-4397-9dbb-9b2b20218538
DevTools: reset inspector agents before frame view is reset, but after the rest of the frame interations.

BUG=352702,312393,344623

Review URL: https://codereview.chromium.org/204543004

git-svn-id: svn://svn.chromium.org/blink/trunk@169791 bbb929c8-8fbe-4397-9dbb-9b2b20218538