Only Register() platform specific content settings types on different platforms

components/content_settings/core/browser/website_settings_info.h

Index: components/content_settings/core/browser/website_settings_info.h
diff --git a/components/content_settings/core/browser/website_settings_info.h b/components/content_settings/core/browser/website_settings_info.h
index 762e32e828c4e52f58a802817d527fdb920a9297..04228619628ffc6016339ef80d8a83a477068b62 100644
--- a/components/content_settings/core/browser/website_settings_info.h
+++ b/components/content_settings/core/browser/website_settings_info.h
@@ -50,6 +50,29 @@ class WebsiteSettingsInfo {
     DONT_INHERIT_IN_INCOGNITO,
   };
 
+  // TODO(lshang): Remove this enum when content settings can be registered from
+  // within the component in which they are used. When this is possible then
+  // ifdefs can be contained within each component.
+  enum Platform : uint32_t {
+    PLATFORM_WINDOWS = 1 << 0,
+    PLATFORM_LINUX = 1 << 1,
+    PLATFORM_CHROMEOS = 1 << 2,
+    PLATFORM_MAC = 1 << 3,
+    PLATFORM_ANDROID = 1 << 4,
+    PLATFORM_IOS = 1 << 5,
+
+    // Settings applied to all platforms, including win, mac, linux, chromeos,
+    // android, ios.
+    ALL_PLATFORMS = PLATFORM_WINDOWS | PLATFORM_LINUX | PLATFORM_CHROMEOS |

[msramek, 2016/05/23 14:49:49]

nit: Switching order and defining ALL_PLATFORMS = DESKTOP | PLATFORM_ANDROID |
PLATFORM_IOS would be perhaps more readable.

[lshang, 2016/05/24 11:55:46]

Done.

+                    PLATFORM_MAC |
+                    PLATFORM_ANDROID |
+                    PLATFORM_IOS,
+
+    // Settings only applied to win, mac, linux and chromeos.
+    DESKTOP =
+        PLATFORM_WINDOWS | PLATFORM_LINUX | PLATFORM_CHROMEOS | PLATFORM_MAC,
+  };
+
   WebsiteSettingsInfo(ContentSettingsType type,

[msramek, 2016/05/23 14:49:49]

There is one more irregularity that we should take care of - on iOS, we only
have default settings, but not exceptions.

WebsiteSettingsInfo registers both preferences with PrefService, so it should be
also aware of the platform and *not* register exceptions on iOS.

And to avoid things randomly blowing up, perhaps we should instead just register
exceptions as unsyncable.

[lshang, 2016/05/24 11:55:46]

I made it unsyncable on ios, am I addressing it right?

[msramek, 2016/05/24 14:29:23]

What I meant is that iOS *does* use the default settings for cookies and popups,
just not exceptions. And those two are stored in different prefs. So we could
sync the default setting pref to iOS (the one handled by DefaultProvider), but
unsync the exception pref (defined in PrefProvider).

We could, for example, #ifdef out PrefProvider in HostContentSettingsMap, or
#ifdef the RegisterProfilePrefs call in PrefProvider to always use UNSYNCABLE on
iOS.

But now that I'm thinking about it, the added complexity might not be worth
syncing the two default values. We can address that once (if?) we have proper
content settings on iOS. Let's go with your solution for now.

                       const std::string& name,
                       std::unique_ptr<base::Value> initial_default_value,