Make CompositeEditCommand::cloneParagraphUnderNewElement() to work when |outerNode| doesn't contain |start|

Before this patch, CompositeEditCommand::cloneParagraphUnderNewElement() tried to copy ancestry nodes from |start| to Document node when |start| position isn't in |outerNode|. This patch changes CompositeEditCommand::cloneParagraphUnderNewElement() to copy |start| to |outerNode| only if |outerNode| contains |start| position.

BUG=312529
TEST=LayoutTests/editing/execCommand/indent-with-uneditable-crash.html

Review URL: https://codereview.chromium.org/61723007

git-svn-id: svn://svn.chromium.org/blink/trunk@161762 bbb929c8-8fbe-4397-9dbb-9b2b20218538