Roll pdfium, add GN build for pdf and pdfium.

DEPS

 # This file is automatically processed to create .DEPS.git which is the file
 # that gclient uses under git.
 #
 # See http://code.google.com/p/chromium/wiki/UsingGit
 #
 # To test manually, run:
 #   python tools/deps2git/deps2git.py -o .DEPS.git -w <gclientdir>
 # where <gcliendir> is the absolute path to the directory containing the
 # .gclient file (the parent of "src").
 #
@@ skipping 58 matching lines @@
   # the commit queue can handle CLs rolling ANGLE
   # and whatever else without interference from each other.
   "angle_revision": "d7e7d735ec75a6b0ff855447b20691c7fbb6c97e",
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling build tools
   # and whatever else without interference from each other.
   "buildtools_revision": "5d89977ce55240995d1596fe420b818468f5ec37",
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling PDFIum
   # and whatever else without interference from each other.
-  "pdfium_revision": "dbd4c06036f42d8dffe033ba112d6d7085dfe475",
+  "pdfium_revision": "d68f9a3e646555e292a1f184560149e8a3e629ac",
 }
 
 deps = {
   "src/breakpad/src":
     (Var("googlecode_url") % "google-breakpad") + "/trunk/src@1331",
 
   "src/buildtools":
     Var("chromium_git") + "/chromium/buildtools.git@" +
      Var("buildtools_revision"),
 
@@ skipping 684 matching lines @@
                 "-s", "src/third_party/drmemory/drmemory-windows-sfx.exe.sha1",
               ],
   },
   {
     # A change to a .gyp, .gypi, or to GYP itself should run the generator.
     "name": "gyp",
     "pattern": ".",
     "action": ["python", "src/build/gyp_chromium"],
   },
 ]