Fix scrollbar painting problems in pdf files in HiDPI mode with fractional scales.

Fix scrollbar painting problems in pdf files in HiDPI mode with fractional scales.

Reason for the bug is painting code in the pdf plugin which converts back and forth from pixels to DIP
and back to pixels causing us to draw over the scrollbars. Division and multiplication with fractional scales
Is a lossy operation.


BUG=399150
TEST=Tested manually with fractional scales on Windows.

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=287952

[ananta, 2014-08-02 00:27:39]

+jhorwich

[ananta, 2014-08-06 22:51:15]

+gene

[gene, 2014-08-06 22:55:13]

lgtm

[ananta, 2014-08-06 23:06:16]

The CQ bit was checked by ananta@chromium.org

[commit-bot: I haz the power, 2014-08-06 23:11:53]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/ananta@chromium.org/437873002/20001

[commit-bot: I haz the power, 2014-08-07 02:23:54]

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

[commit-bot: I haz the power, 2014-08-07 03:24:29]

Change committed as 287952