Have EditCommand classes deal with Document references, not pointers

Have EditCommand classes deal with Document references, not pointers

Have EditCommand classes deal with Document references, not pointers, as it
can never be NULL.

BUG=281400
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=157085

[dglazkov, 2013-09-02 15:13:52]

rslgtm.

[commit-bot: I haz the power, 2013-09-02 15:15:24]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/ch.dumez@sisa.samsung.com/23822003/1

[commit-bot: I haz the power, 2013-09-02 15:36:47]

Change committed as 157085