Generalize the flip origin argument to the PDF device constructor.

Generalize the flip origin argument to the PDF device constructor.

The argument still has a default value that does what most users will want, but provides more flexibility.
Chrome will use this change to support an initial translation of the origin to simulate a margin and to scale the entire content (needed on Windows).

When landing to Chrome, this will need http://codereview.chromium.org/6820038

Review URL: http://codereview.appspot.com/4373052

git-svn-id: http://skia.googlecode.com/svn/trunk@1111 2bbb7eff-a529-9590-31e7-b0007b416f81