Do not disable warnings-as-errors for pdfium.

pdfium.gyp

 {
   'variables': {
-    'win_third_party_warn_as_error': 'false',
     'pdf_use_skia%': 0,
   },
   'target_defaults': {
     'defines' : [
       'FOXIT_CHROME_BUILD',
       '_FXFT_VERSION_=2501',
       '_FPDFSDK_LIB',
       '_NO_GDIPLUS_',  # workaround text rendering issues on Windows
     ],
     'conditions': [
@@ skipping 16 matching lines @@
           ['target_arch=="ia32"', {
             'defines' : [
               '_FX_CPU_=_FX_X86_',
             ],
           }],
         ],
       }],
       ['OS=="mac"', {
         'xcode_settings': {
           'GCC_ENABLE_CPP_EXCEPTIONS': 'YES',
-          'GCC_TREAT_WARNINGS_AS_ERRORS': 'NO',    # -Werror
         },
       }],
-      ['clang==1', {
-         'cflags!': [
-           '-Werror',
-         ],
-      }],
     ],
     'msvs_disabled_warnings': [
       4005, 4018, 4146, 4333, 4345
     ],
   },
   'targets': [
     {
       'target_name': 'pdfium',
       'type': 'static_library',
       'dependencies': [
@@ skipping 798 matching lines @@
         'fpdfsdk/src/formfiller/FFL_ListBox.cpp',
         'fpdfsdk/src/formfiller/FFL_Notify.cpp',
         'fpdfsdk/src/formfiller/FFL_PushButton.cpp',
         'fpdfsdk/src/formfiller/FFL_RadioButton.cpp',
         'fpdfsdk/src/formfiller/FFL_TextField.cpp',
         'fpdfsdk/src/formfiller/FFL_Utils.cpp',
       ],
     },
   ],
 }