[PDF] Add unpremultiply support and a GM.

This is a resubmit of https://codereview.chromium.org/22831039 which was
reverted because it causes issues on Windows.

BUG=chromium:175548
R=edisonn@google.com

Review URL: https://codereview.chromium.org/27518003

git-svn-id: http://skia.googlecode.com/svn/trunk/gyp@11857 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/gmslides.gypi b/gmslides.gypi
index a83ae2e..4591346 100644
--- a/gmslides.gypi
+++ b/gmslides.gypi
@@ -15,6 +15,7 @@
     '../gm/bitmapcopy.cpp',
     '../gm/bitmapmatrix.cpp',
     '../gm/bitmapfilters.cpp',
+    '../gm/bitmappremul.cpp',
     '../gm/bitmaprect.cpp',
     '../gm/bitmaprecttest.cpp',
     '../gm/bitmapscroll.cpp',