Oilpan: add SVGRemoteFontFaceSource::trace().

R=kouhei@chromium.org,haraken@chromium.org
BUG=357163

Review URL: https://codereview.chromium.org/298863009

git-svn-id: svn://svn.chromium.org/blink/trunk@174670 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Don't indent if selection is none.

ApplyBlockElementCommand::doApply() assumes selection to indent points non-null
position. However, there is a chance this assumption is false, e.g. HTML used
in "indent-button-crash.html".

This patch makes ApplyBlockElementCommand::doApply() to check whether assumption
is satisfied or not.

BUG=368133
TEST=LayoutTests/editing/execCommand/indent-button-crash.html

Review URL: https://codereview.chromium.org/291143002

git-svn-id: svn://svn.chromium.org/blink/trunk@174671 bbb929c8-8fbe-4397-9dbb-9b2b20218538