FrameSelection::textWasReplaced and setSelectedRange shouldn't trigger synchronous layout

These synchronous calls to layout aren't necessary.

This CL merges http://trac.webkit.org/changeset/164319 by rniwa, which made WebKit go
fast on Speedometer.

BUG=380173

Review URL: https://codereview.chromium.org/315663006

git-svn-id: svn://svn.chromium.org/blink/trunk@175421 bbb929c8-8fbe-4397-9dbb-9b2b20218538