Make redo command not to set invalid selection

This patch makes "redo" command not to set invalid selection to |FrameSeleciton|
via |Editor::changeSelectionAfterCommand()| to avoid |DCHECK()| in
|FrameSelection::setSelection()|.

BUG=623241
TEST=LayoutTests/editing/undo/redo-selection-modify-crash.html

Review-Url: https://codereview.chromium.org/2120223002
Cr-Commit-Position: refs/heads/master@{#403657}
2 files changed