Don't add BR when pruning empty blocks if it's the start of a paragraph

The function MoveParagraph is used for several operations and editing
commands, like 'insertOrderedList'. When moving paragraphs we check out
whether we should add a 'br' element to avoid undesired block collapse.

However, we shouldn't do this when destination is the start of a
paragraph.

Bug: 744936
Change-Id: I366b903b5f3737bd6c84e9fc8c91a4894ca680af
Reviewed-on: https://chromium-review.googlesource.com/581008
Commit-Queue: Javier Fernandez <jfernandez@igalia.com>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#493504}
4 files changed