Add namespace and re-arrange PDFium's local copy of chromium /base.

pdfium.gyp

 {
   'variables': {
     'pdf_use_skia%': 0,
     'conditions': [
       ['OS=="linux"', {
         'bundle_freetype%': 0,
       }, {  # On Android there's no system FreeType. On Windows and Mac, only a
             # few methods are used from it.
         'bundle_freetype%': 1,
       }],    
@@ skipping 27 matching lines @@
     'msvs_disabled_warnings': [
       4005, 4018, 4146, 4333, 4345, 4267
     ],
   },
   'targets': [
     {
       'target_name': 'pdfium',
       'type': 'static_library',
       'dependencies': [
         'third_party/third_party.gyp:bigint',
-        'third_party/third_party.gyp:safemath',
+        'third_party/third_party.gyp:pdfium_base',
         'fdrm',
         'fpdfdoc',
         'fpdfapi',
         'fpdftext',
         'formfiller',
         'fxcodec',
         'fxcrt',
         'fxedit',
         'fxge',
         'javascript',
@@ skipping 800 matching lines @@
         'fpdfsdk/src/fpdftext_embeddertest.cpp',
         'fpdfsdk/src/fpdfview_embeddertest.cpp',
         'testing/embedder_test.cpp',
         'testing/embedder_test.h',
         'testing/fx_string_testhelpers.cpp',
         'testing/fx_string_testhelpers.h',
       ],
     },
   ],
 }