Add initial libfuzzers for fm2js transpiling and XML parsing.

testing/libfuzzer/BUILD.gn

+# Copyright 2016 The PDFium 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("../../pdfium.gni")
+
+config("libfuzzer_config") {
+  defines = [
+    "PNG_PREFIX",
+    "PNGPREFIX_H",
+    "PNG_USE_READ_MACROS",
+  ]
+  include_dirs = [ "../.." ]
+  if (pdf_enable_v8) {
+    defines += [ "PDF_ENABLE_V8" ]
+  }
+  if (pdf_enable_xfa) {
+    defines += [ "PDF_ENABLE_XFA" ]
+  }
+}
+
+if (pdf_enable_xfa) {
+  source_set("pdf_fm2js_fuzzer") {
+    testonly = true
+    sources = [
+      "pdf_fm2js_fuzzer.cc",
+    ]
+    deps = [
+      "//third_party/pdfium:pdfium",
+    ]
+    configs -= [ "//build/config/compiler:chromium_code" ]
+    configs += [
+      "//build/config/compiler:no_chromium_code",
+      ":libfuzzer_config",
+    ]
+  }
+  source_set("pdf_xml_fuzzer") {
+    testonly = true
+    sources = [
+      "pdf_xml_fuzzer.cc",
+    ]
+    deps = [
+      "//third_party/pdfium:pdfium",
+    ]
+    configs -= [ "//build/config/compiler:chromium_code" ]
+    configs += [
+      "//build/config/compiler:no_chromium_code",
+      ":libfuzzer_config",
+    ]
+  }
+}