Possible deferencing from nullptrs in AtkComponent interface.

Possible deferencing from nullptrs in AtkComponent interface.

Make sure AtkComponent interface callbacks operate on valid pointers.
GetExtent and GetPosition are almost the same. Reducing some code
by adding helper method SetExtentsRelativeToAtkCoordinateType.

BUG=463671
Committed: https://crrev.com/98cb52ed6cc58b257d590ef1cfe9e83eb1b01d1a
Cr-Commit-Position: refs/heads/master@{#329664}

[k.czech, 2015-05-12 22:59:05]

k.czech@samsung.com changed reviewers:
+ dmazzoni@chromium.org, shreeram.k@samsung.com

[dmazzoni, 2015-05-13 16:42:20]

The CQ bit was checked by dmazzoni@chromium.org

[dmazzoni, 2015-05-13 16:42:20]

lgtm

[commit-bot: I haz the power, 2015-05-13 16:42:55]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1129813004/1

[commit-bot: I haz the power, 2015-05-13 17:23:09]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-13 17:23:51]

Patchset 1 (id:??) landed as
https://crrev.com/98cb52ed6cc58b257d590ef1cfe9e83eb1b01d1a
Cr-Commit-Position: refs/heads/master@{#329664}