Turn on -Wall -Wextra on Mac, and fix all the warnings that crop up for /usr/bin/g++ and Clang 3.3.

gyp/common_conditions.gypi

 # conditions used in both common.gypi and skia.gyp in chromium
 #
 {
   'defines': [
     'SK_ALLOW_STATIC_GLOBAL_INITIALIZERS=<(skia_static_initializers)',
 #    'SK_SUPPORT_HINTING_SCALE_FACTOR',
   ],
   'conditions' : [
     [ 'skia_gpu == 1',
       {
@@ skipping 288 matching lines @@
           }],
           [ 'skia_arch_width == 32', {
             'xcode_settings': {
               'ARCHS': ['i386'],
             },
           }],
           [ 'skia_warnings_as_errors', {
             'xcode_settings': {
               'OTHER_CPLUSPLUSFLAGS': [
                 '-Werror',
+                '-Wall',
+                '-Wextra',
+                '-Wno-unused-parameter',
               ],
             },
           }],
         ],
         'configurations': {
           'Debug': {
             'xcode_settings': {
               'GCC_OPTIMIZATION_LEVEL': '0',
             },
           },
@@ skipping 145 matching lines @@
   'xcode_settings': {
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }
 
 # Local Variables:
 # tab-width:2
 # indent-tabs-mode:nil
 # End:
 # vim: set expandtab tabstop=2 shiftwidth=2: