[subresource_filter] Swap ALLOW and BLOCK meanings in the content setting

components/content_settings/core/browser/content_settings_registry.cc

Index: components/content_settings/core/browser/content_settings_registry.cc
diff --git a/components/content_settings/core/browser/content_settings_registry.cc b/components/content_settings/core/browser/content_settings_registry.cc
index 217e0a8eb282365058ac9a83f1cf7ba6543894c8..6b18f449543cacb3ce70e237a93f088ee631506d 100644
--- a/components/content_settings/core/browser/content_settings_registry.cc
+++ b/components/content_settings/core/browser/content_settings_registry.cc
@@ -275,8 +275,8 @@ void ContentSettingsRegistry::Init() {
            ContentSettingsInfo::INHERIT_IF_LESS_PERMISSIVE);
 
   Register(CONTENT_SETTINGS_TYPE_SUBRESOURCE_FILTER, "subresource-filter",
-           CONTENT_SETTING_ALLOW,
-           WebsiteSettingsInfo::UNSYNCABLE, WhitelistedSchemes(),
+           CONTENT_SETTING_BLOCK, WebsiteSettingsInfo::UNSYNCABLE,

[engedy, 2017/05/11 10:39:37]

Changing the default value for a content setting is safe and supported, right?

[Charlie Harrison, 2017/05/11 14:05:44]

AFAICT this is safe since default values are not persisted on disk (anywhere I
can see).

raymes: can you confirm?

[msramek, 2017/05/11 14:29:20]

The default provider currently doesn't distinguish between users who had ALLOW
because they never touched it, and those who had ALLOW explicitly (i.e. by
switching to BLOCK and back).

So after this change, everyone who had ALLOW will have BLOCK, and everyone who
had BLOCK will also have BLOCK.

But it won't crash anything.

If you care about users who might have already started using this, you should
add a migration code to PrefProvider (default BLOCK->ALLOW), and PrefProvider
(mirror all exceptions).

[Charlie Harrison, 2017/05/11 15:50:11]

Thanks for the clarification. As discussed offline, we probably don't need a
migration path since this isn't being used outside of our own dev builds.

+           WhitelistedSchemes(),
            ValidSettings(CONTENT_SETTING_ALLOW, CONTENT_SETTING_BLOCK),
            WebsiteSettingsInfo::REQUESTING_ORIGIN_ONLY_SCOPE,
            WebsiteSettingsRegistry::DESKTOP |