pdfviewer: more code comments + concat the pdf matrix with the existing matrix in canvas, instead of reseting it.

Review URL: https://codereview.chromium.org/27057003

git-svn-id: http://skia.googlecode.com/svn/trunk@11735 2bbb7eff-a529-9590-31e7-b0007b416f81
10 files changed