Make sure calling moveParagaph() with proper parameters in CompositeEditCommand::moveParagraphContentsToNewBlockIfNecessary()

This patch changes CompositeEditCommand::moveParagraphContentsToNewBlockIfNecessary()
to calculate start and end positions of paragraph to move before calling
moveParagraph(), because inserting paragraph element at |upstream| can change
start and end positions represented by |VisiblePosition|.

This patch is similar to http://crrev.com/311593003, for
InsertListCommand::listifyParagraph().

BUG=325222, 351291
TEST=LayoutTests/editing/execCommand/apply-style-empty-paragraph-start-crash.html

Review URL: https://codereview.chromium.org/315513003

git-svn-id: svn://svn.chromium.org/blink/trunk@175523 bbb929c8-8fbe-4397-9dbb-9b2b20218538