Merge to XFA: Fix all relative includes to third_party.

samples/samples.gyp

 # Copyright 2014 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,
   },
   'target_defaults': {
     'type': 'executable',
     'dependencies': [
       '../pdfium.gyp:pdfium',
     ],
     'include_dirs': [
       '<(DEPTH)',
     ],
     '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',
         ],
       }],
@@ skipping 20 matching lines @@
       ],
     },
     {
       'target_name': 'pdfium_diff',
       'type': 'executable',
       'variables': { 'enable_wexit_time_destructors': 1, },
       'dependencies': [
         '../pdfium.gyp:fxcodec',
         '../third_party/third_party.gyp:pdfium_base',
       ],
-      'include_dirs': [
-        '../../',
-      ],
       'sources': [
         'image_diff.cc',
         'image_diff_png.h',
         'image_diff_png.cc',
       ],
     },
   ],
 }