Fix double-offset issue of RenderObject::positionFromPaintInvalidationContainer()

Fix double-offset issue of RenderObject::positionFromPaintInvalidationContainer()

As currently we only use positionFromPaintInvalidationContainer to
check if it has changed, neither the issue nor the fix visibly affects
any behavior.

The fix is required by https://codereview.chromium.org/399173005.

Also removed roundedIntPoint because now we pass sub-pixel coordinates
to GraphicsLayer for invalidations
(after https://codereview.chromium.org/353403006/).

BUG=395217
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=178503

[Julien - ping for review, 2014-07-18 21:23:03]

lgtm

[commit-bot: I haz the power, 2014-07-18 21:24:15]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/wangxianzhu@chromium.org/408483005/1

[Xianzhu, 2014-07-18 22:16:13]

The CQ bit was checked by wangxianzhu@chromium.org

[commit-bot: I haz the power, 2014-07-18 22:16:15]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/wangxianzhu@chromium.org/408483005/20001

[commit-bot: I haz the power, 2014-07-18 23:37:54]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/17822)

[commit-bot: I haz the power, 2014-07-19 00:10:27]

Change committed as 178503