Roll PDFium

This brings in:

28ddd48  Replace second set of #defines with templates in JS_Define.h
94dd28e  Update GN build files w/ cpu_arch -> current_cpu changes.
dce5730  Add test for PDF's JS "global".
a96cc9b  Replace ugly JS_Define macros with templates.
2da7bd4  Tidy up JS_Defines.h
7435e8e  Run pixel tests via automated script.
83c87e5  run_javascript_tests.py: Be more flexible about directory layout.

TBR=jam@chromium.org, tsepez@chromium.org
BUG=344767

Review URL: https://codereview.chromium.org/948933003

Cr-Commit-Position: refs/heads/master@{#317684}

DEPS

@@ -67,7 +67,7 @@ vars = {
   # 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': '58985096a7852263df68e87d9bfc335a3e2759bf',
+  'pdfium_revision': '28ddd48bfd84c55cc51d0b16fa533c51affdeb5b',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling openmax_dl
   # and whatever else without interference from each other.