Add unit test for fdrm's MD5

BUILD.gn

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build_overrides/v8.gni")
 import("//testing/test.gni")
 import("pdfium.gni")
 
 config("pdfium_common_config") {
   cflags = []
@@ skipping 1679 matching lines @@
     ]
     configs += [
       ":pdfium_core_config",
       ":xfa_warnings",
     ]
   }
 }
 
 test("pdfium_unittests") {
   sources = [
+    "core/fdrm/crypto/fx_crypt_unittest.cpp",
     "core/fpdfapi/font/fpdf_font_cid_unittest.cpp",
     "core/fpdfapi/font/fpdf_font_unittest.cpp",
     "core/fpdfapi/page/cpdf_streamcontentparser_unittest.cpp",
     "core/fpdfapi/page/cpdf_streamparser_unittest.cpp",
     "core/fpdfapi/parser/cpdf_array_unittest.cpp",
     "core/fpdfapi/parser/cpdf_document_unittest.cpp",
     "core/fpdfapi/parser/cpdf_object_unittest.cpp",
     "core/fpdfapi/parser/cpdf_parser_unittest.cpp",
     "core/fpdfapi/parser/cpdf_simple_parser_unittest.cpp",
     "core/fpdfapi/parser/cpdf_syntax_parser_unittest.cpp",
@@ skipping 118 matching lines @@
       "//samples",
     ]
   }
   group("fuzzers") {
     testonly = true
     deps = [
       "//testing/libfuzzer",
     ]
   }
 }