In windows printing, convert src bitmap to dest bitmap using CompositeBitmap.

In windows printing, convert src bitmap to dest bitmap using CompositeBitmap.

When dealing with transparency, the printing procedure will generate a bitmap first,
then draw this bitmap in windows DC.
The format of source bitmap is argb, but the destination bitmap is rgb.
Simply doing memcpy will lose the alpha channel information, so CompositeBitmap function is needed.

BUG=412908
R=vitalybuka@chromium.org

Committed: https://pdfium.googlesource.com/pdfium/+/07f10ae2eede1ad1fbb4424064eaaaa77dfb90d2

[Bo Xu, 2014-12-24 06:30:22]

bo_xu@foxitsoftware.com changed reviewers:
+ vitalybuka@chromium.org

[Bo Xu, 2014-12-24 06:30:22]

Hi Vitaly, please take a look at this CL. Thanks!

[Bo Xu, 2014-12-30 18:09:29]

On 2014/12/24 06:30:22, Bo Xu wrote:
> Hi Vitaly, please take a look at this CL. Thanks!

Ping :)

[Vitaly Buka (NO REVIEWS), 2015-01-05 05:35:13]

lgtm

[Bo Xu, 2015-01-05 18:12:11]

Committed patchset #1 (id:1) manually as
07f10ae2eede1ad1fbb4424064eaaaa77dfb90d2 (presubmit successful).