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..fac4d99edc59817316d2bd5056995135b70d107d 100644
--- a/components/content_settings/core/browser/website_settings_info.h
+++ b/components/content_settings/core/browser/website_settings_info.h
@@ -50,6 +50,21 @@ class WebsiteSettingsInfo {
     DONT_INHERIT_IN_INCOGNITO,
   };
 
+  enum AppliedPlatform {

[raymes, 2016/05/20 19:10:16]

nit: Maybe just Platform?

I wonder if we should move this into WebsiteSettingsRegistry since it's not
actually used in this file.

It feels like we should have a bitmask here with DESKTOP defined in terms of
windows, linux, chromeos and mac. It would make the code which checks the
platform simpler and it would avoid having to add more values to this enum in
the future. I don't think it would be much more complicated. See e.g.
https://code.google.com/p/chromium/codesearch#chromium/src/components/pref_re...

Also as I thought about it more I'm not sure this is a good long-term solution.
I think long term each content setting should be registered from within the
component/code where it is used. Then each component could ifdef its own content
settings depending on the platforms on which the component is used. That is a
more modular approach. However I think this is good for now. Let's add a TODO,
something like:
// TODO(...): 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.

[lshang, 2016/05/24 11:55:45]

Done.

+    // Settings applied to all platforms, including win, mac, linux, chromeos,
+    // android, ios.
+    ALL_PLATFORMS,
+
+    // Settings only applied to win, mac, linux and chromeos.
+    DESKTOP_ONLY,
+
+    // Settings applied to win, mac, linux, chromeos and android, but not ios.
+    DESKTOP_AND_ANDROID_ONLY,
+
+    // Settings only applied to android and chromeos.
+    ANDROID_AND_CHROMEOS_ONLY
+  };
+
   WebsiteSettingsInfo(ContentSettingsType type,
                       const std::string& name,
                       std::unique_ptr<base::Value> initial_default_value,