Cleanup: Remove unused pdf resource header files.

pdf/pdf.gyp

 {
   'variables': {
     'chromium_code': 1,
     'pdf_engine%': 0,  # 0 PDFium
   },
   'targets': [
     {
       'target_name': 'pdf',
       'type': 'static_library',
       'dependencies': [
@@ skipping 18 matching lines @@
         'out_of_process_instance.h',
         'paint_aggregator.cc',
         'paint_aggregator.h',
         'paint_manager.cc',
         'paint_manager.h',
         'pdf.cc',
         'pdf.h',
         'pdf_engine.h',
         'preview_mode_client.cc',
         'preview_mode_client.h',
-        'resource.h',
-        'resource_consts.h',
       ],
       'conditions': [
         ['pdf_engine==0', {
           'sources': [
             'pdfium/pdfium_api_string_buffer_adapter.cc',
             'pdfium/pdfium_api_string_buffer_adapter.h',
             'pdfium/pdfium_assert_matching_enums.cc',
             'pdfium/pdfium_engine.cc',
             'pdfium/pdfium_engine.h',
             'pdfium/pdfium_mem_buffer_file_read.cc',
             'pdfium/pdfium_mem_buffer_file_read.h',
             'pdfium/pdfium_mem_buffer_file_write.cc',
             'pdfium/pdfium_mem_buffer_file_write.h',
             'pdfium/pdfium_page.cc',
             'pdfium/pdfium_page.h',
             'pdfium/pdfium_range.cc',
             'pdfium/pdfium_range.h',
           ],
         }],
         ['OS=="win"', {
           # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
           'msvs_disabled_warnings': [ 4267, ],
         }],
       ],
     },
   ],
 }