Roll pdfium to a48ead9b7e3dc01f1bde83f69062eebd960edfdc.

This bring in:
a48ead9 Re-enable pdfium_unittests.
dd132d8 Update externs in unicodenormalization.cpp to not have array sizes.
c5f520c Get rid of g_timeMap global object.
f964049 Fix an array size mismatch.
286ea1d Remove run-time calculation of hash constants in pdfium.
a975cfa Get rid of fifteen copies of m_sTimeMap and their initializers.
2638428 Clean up bookmark related codes.
17b5cf4 Remove static declared SymbolDictCache.
07f10ae In windows printing, convert src bitmap to dest bitmap using CompositeBitmap.
d66051b Remove g_NaN global variable and its constructor.
659a56b Get rid of FX_LPCSTR cast.
3fc36e8 Revert build of pdfium_unittests.
831e138 Fix pdfium buildbot build breakage from 336991d.
336991d Create pdfium_unittests binary.
6c06469 Refactor some code in CPDF_TextPage::ProcessTextObject().
59dffb6 Fix new third_party/BUILD.gn to use the right build configuration.
06b087a Set the freetype options missing in the recent update.
b3a3230 Add the license back to ftmodule.h after the freetype 2.5.4 upgrade.
a09d50d Transform font size to user space for valid text size comparison.
e4fc5ce Update freetype to 2.5.4.

Review URL: https://codereview.chromium.org/789613007

Cr-Commit-Position: refs/heads/master@{#310158}

DEPS

@@ -68,7 +68,7 @@ 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': '5a35129bce7ca777e155e5498e8d4792fa6a4819',
+  'pdfium_revision': 'a48ead9b7e3dc01f1bde83f69062eebd960edfdc',
   # 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.