Fix crash in CompositeEditCommand::cloneParagraphUnderNewElement()

Fix crash in CompositeEditCommand::cloneParagraphUnderNewElement()
<http://webkit.org/b/129751>
<rdar://problem/16237965>

Reviewed by Jon Honeycutt.

Merged from Blink (patch by Yuta Kitamura):
https://src.chromium.org/viewvc/blink?revision=168160&view=revision
http://crbug.com/345005

    The root cause is CompositeEditCommand::moveParagraphWithClones() passing
    two positions |start| and |end| which do not follow the document order,
    i.e. in some situations |start| is located after |end| because of
    the difference in affinity.

    This patch fixes this crash by normalizing |end| to |start| in such situations.
    It also adds an ASSERT that checks the relationship between |start| and |end|.

Source/WebCore:

Test: editing/execCommand/format-block-crash.html

* editing/CompositeEditCommand.cpp:
(WebCore::CompositeEditCommand::cloneParagraphUnderNewElement):
(WebCore::CompositeEditCommand::moveParagraphWithClones):
* editing/CompositeEditCommand.h:

LayoutTests:

* editing/execCommand/format-block-crash-expected.txt: Added.
* editing/execCommand/format-block-crash.html: Added.
* editing/execCommand/resources/format-block-crash-iframe.html: Added.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@165138 268f45cc-cd09-0410-ab3c-d52691b4dbfc