Add metrics for schemes of content setting exceptions

components/content_settings/core/browser/host_content_settings_map.cc

Index: components/content_settings/core/browser/host_content_settings_map.cc
diff --git a/components/content_settings/core/browser/host_content_settings_map.cc b/components/content_settings/core/browser/host_content_settings_map.cc
index 1805e9cd1b74760f6b71f821e12adf3522e6d18c..555133ffe898be43509cab3b2046a93c7d1e2735 100644
--- a/components/content_settings/core/browser/host_content_settings_map.cc
+++ b/components/content_settings/core/browser/host_content_settings_map.cc
@@ -187,7 +187,7 @@ HostContentSettingsMap::HostContentSettingsMap(PrefService* prefs,
 
   MigrateKeygenSettings();
   MigrateDomainScopedSettings(false);
-  RecordNumberOfExceptions();
+  RecordExceptionMetrics();
 }
 
 // static
@@ -600,7 +600,7 @@ base::WeakPtr<HostContentSettingsMap> HostContentSettingsMap::GetWeakPtr() {
   return weak_ptr_factory_.GetWeakPtr();
 }
 
-void HostContentSettingsMap::RecordNumberOfExceptions() {
+void HostContentSettingsMap::RecordExceptionMetrics() {
   for (const content_settings::WebsiteSettingsInfo* info :
        *content_settings::WebsiteSettingsRegistry::GetInstance()) {
     ContentSettingsType content_type = info->type();
@@ -610,6 +610,13 @@ void HostContentSettingsMap::RecordNumberOfExceptions() {
     GetSettingsForOneType(content_type, std::string(), &settings);
     size_t num_exceptions = 0;
     for (const ContentSettingPatternSource& setting_entry : settings) {
+      // Skip default settings.
+      if (setting_entry.primary_pattern != ContentSettingsPattern::Wildcard()) {

[msramek, 2016/08/08 17:33:12]

nit: Should we also check the secondary pattern for a wildcard? Not sure if that
can actually happen but it at least makes the intention clearer.

[lshang, 2016/08/09 01:56:40]

Done.

+        UMA_HISTOGRAM_ENUMERATION("ContentSettings.ExceptionScheme",

[msramek, 2016/08/08 17:33:12]

We're recording exceptions from all sources - including policy, extensions etc.
Is that intentional?

[lshang, 2016/08/09 01:56:40]

I think we would want to collect scheme data from all sources including policy
and extensions, if we want to see the effect of removing support for file://
schemes. Please see background details above.

[msramek, 2016/08/09 10:47:43]

Acknowledged. Yes, that makes sense now that I read about the background.

+                                  setting_entry.primary_pattern.GetScheme(),
+                                  ContentSettingsPattern::SCHEME_MAX);
+      }
+
       if (setting_entry.source == "preference")
         ++num_exceptions;
     }