Add initial libfuzzers for fm2js transpiling and XML parsing.

testing/libfuzzer/fuzzers.gyp

+# Copyright 2016 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.
+
+{
+  'variables': {
+    'pdf_enable_v8%': 1,
+    'pdf_enable_xfa%': 0,  # Set to 1 in standalone builds by standalone.gypi.
+  },
+  'target_defaults': {
+    'defines' : [
+      'PNG_PREFIX',
+      'PNGPREFIX_H',
+      'PNG_USE_READ_MACROS',
+    ],
+    'include_dirs': [
+      # This is implicit in GN.
+      '<(DEPTH)',
+    ],
+    'conditions': [
+      ['pdf_enable_v8==1', {
+        'defines': [
+          'PDF_ENABLE_V8',
+        ],
+        'include_dirs': [
+          '<(DEPTH)/v8',
+          '<(DEPTH)/v8/include',
+        ],
+      }],
+      ['pdf_enable_xfa==1', {
+        'defines': [
+          'PDF_ENABLE_XFA',
+        ],
+      }],
+    ],
+  },
+  'conditions': [
+    ['pdf_enable_xfa==1 and OS!="win"', {
+      'targets': [
+        {
+          'target_name': 'pdf_fm2js_fuzzer',
+          'type': 'executable',
+          'dependencies': [
+            '../../pdfium.gyp:pdfium',
+          ],
+          'sources': [
+            'pdf_fm2js_fuzzer.cc',
+            'unittest_main.cc',
+          ],
+        },
+        {
+          'target_name': 'pdf_xml_fuzzer',
+          'type': 'executable',
+          'dependencies': [
+            '../../pdfium.gyp:pdfium',
+          ],
+          'sources': [
+            'pdf_xml_fuzzer.cc',
+            'unittest_main.cc',
+          ],
+        },
+      ],
+    }],
+  ]
+}