Don't call splitTreeToNode() with null Node

Don't call splitTreeToNode() with null Node

This patch changes |IndentOutdentCommand::outdentParagraph()| to check whether
|enclosingBlockNode| is null or not, before passing it to
|CompositeEditCommand::splitTreeToNode()| which assumes it isn't null.

This situation can be happened in attach test case, where
|enclosingBlockNode| is calculated from |visibleStartOfParagraph|, which is
second TABLE element, by |enclosingBlock()|.

BUG=378758
TEST=editing/execCommand/outdent-collapse-table-crash.html

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=175251

[yosin_UTC9, 2014-05-30 13:19:54]

Could you review this patch?
Thanks in advance.

Note: blink_android_compile_{dbg,rel} and mac_blink_rel compilation failures
aren't related to this patch.

[yosin_UTC9, 2014-05-30 13:20:36]

Could you review this patch?
Thanks in advance.

Note: blink_android_compile_{dbg,rel} and mac_blink_rel compilation failures
aren't related to this patch.

[Yuta Kitamura, 2014-06-02 03:04:04]

lgtm

[yosin_UTC9, 2014-06-02 03:33:11]

The CQ bit was checked by yosin@chromium.org

[commit-bot: I haz the power, 2014-06-02 03:33:24]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/yosin@chromium.org/308023003/20001

[commit-bot: I haz the power, 2014-06-02 03:34:32]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  blink_presubmit on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/blink_presubmit/builds/6632)

[commit-bot: I haz the power, 2014-06-02 03:45:41]

Change committed as 175251