Remove setNeedsRecalcStyle() in Document::didLoadAllImports().

r173248 added it but there is a performance concern.
This change repalces it with a modest alternative that does same as what didRemoveAllPendingStylesheet() has been doing.

This change also removed 500ms sleep from a test that was added at r173248.

TEST=none
R=ojan@chromium.org,esprehn@chromium.org
BUG=367386

Review URL: https://codereview.chromium.org/279463002

git-svn-id: svn://svn.chromium.org/blink/trunk@173680 bbb929c8-8fbe-4397-9dbb-9b2b20218538