Move implementation of Range::firstNode and Range::pastLastNode to Position

Move implementations of Range::firstNode and Range::pastLastNode to Position

This patch move implementations of |Range::firstNode()| and
|Range::pastLastNode()| to |Position| class to use them via |Position| object
rather than creating |Range| object to use |TextIterator| class and
|createMarkup()| function via |Position| rather than |Range| to avoid creating
temporary |Range| objects, for |document.execCommand("copy").

This patch is a preparation of using composed tree for selection.

BUG=275851
TEST=n/a; no behavior changes

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=191892

[yosin_UTC9, 2015-03-13 07:52:50]

Patchset #1 (id:1) has been deleted

[yosin_UTC9, 2015-03-13 09:21:55]

yosin@chromium.org changed reviewers:
+ tkent@chromium.org

[yosin_UTC9, 2015-03-13 09:21:56]

PTAL

P.S.
Linux bot failures aren't related to this patch.

[tkent, 2015-03-13 09:34:11]

lgtm

[yosin_UTC9, 2015-03-16 01:10:07]

The CQ bit was checked by yosin@chromium.org

[commit-bot: I haz the power, 2015-03-16 01:10:15]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1000533004/20001

[commit-bot: I haz the power, 2015-03-16 04:20:54]

Committed patchset #1 (id:20001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=191892

[sof, 2015-05-05 08:23:22]

sigbjornf@opera.com changed reviewers:
+ sigbjornf@opera.com

[sof, 2015-05-05 08:23:23]

https://codereview.chromium.org/1000533004/diff/20001/Source/core/dom/Range.cpp
File Source/core/dom/Range.cpp (right):

https://codereview.chromium.org/1000533004/diff/20001/Source/core/dom/Range.c...
Source/core/dom/Range.cpp:1417: return
startPosition().toOffsetInAnchor().nodeAsRangeFirstNode();
Is this a meaning-preserving transformation - what if the start node doesn't
have an anchor?

All uses of Range::firstNode() currently crash as a result - addressing via
https://codereview.chromium.org/1121633004/