Define the Settings interface for a CrashReportDatabase and provide a Mac implementation.

client/client.gyp

Index: client/client.gyp
diff --git a/client/client.gyp b/client/client.gyp
index c8895563f80d0a2f563737eaacf02ec0ee84cb74..2cfed50344145ff8cb200e45df8894da8a7d74c3 100644
--- a/client/client.gyp
+++ b/client/client.gyp
@@ -36,6 +36,9 @@
         'crashpad_client_mac.cc',
         'crashpad_info.cc',
         'crashpad_info.h',
+        'settings.h',
+        'settings_mac.h',
+        'settings_mac.mm',
         'simple_string_dictionary.cc',
         'simple_string_dictionary.h',
         'simulate_crash.h',
@@ -70,9 +73,18 @@
       'sources': [
         'capture_context_mac_test.cc',
         'crash_report_database_test.cc',
+        'settings_test.cc',
         'simple_string_dictionary_test.cc',
         'simulate_crash_mac_test.cc',
       ],
+      'conditions': [
+        ['OS=="win"', {
+          'sources!' [
+            # There is no settings_win.cc file yet to make this test pass.
+            'settings_test.cc',
+          ],
+        }],
+      ],
     },
   ],
 }