Mac: implement <keygen> support, including adding generated cert to the Keychain.

net/net.gyp

Index: net/net.gyp
diff --git a/net/net.gyp b/net/net.gyp
index 7cabfc7f2b3d6d181ea260f486691e6ae8de6ddd..e7008a06ffb0f6795771d0fe4d2924c3297abf94 100644
--- a/net/net.gyp
+++ b/net/net.gyp
@@ -596,6 +596,7 @@
         'base/gzip_filter_unittest.cc',
         'base/host_cache_unittest.cc',
         'base/host_resolver_impl_unittest.cc',
+        'base/keygen_handler_unittest.cc',
         'base/load_log_unittest.cc',
         'base/load_log_unittest.h',
         'base/load_log_util_unittest.cc',
@@ -708,9 +709,13 @@
             }],
           ],
         }],
-        # This is needed to trigger the dll copy step on windows.
-        # TODO(mark): Specifying this here shouldn't be necessary.
         [ 'OS == "win"', {
+            'sources!': [
+              # Remove next line when KeygenHandler is implemented for Windows.
+              'base/keygen_handler_unittest.cc',
+            ],
+            # This is needed to trigger the dll copy step on windows.
+            # TODO(mark): Specifying this here shouldn't be necessary.
             'dependencies': [
               '../third_party/icu/icu.gyp:icudata',
             ],