Add metrics for user manually added 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 978aff41c2b478be224d5ca13d801825741151ce..a6b9af22234043504b421513c626f4a85ebde375 100644
--- a/components/content_settings/core/browser/host_content_settings_map.cc
+++ b/components/content_settings/core/browser/host_content_settings_map.cc
@@ -10,6 +10,7 @@
 
 #include "base/command_line.h"
 #include "base/macros.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/stl_util.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
@@ -168,6 +169,8 @@ HostContentSettingsMap::HostContentSettingsMap(PrefService* prefs,
   content_settings_providers_[DEFAULT_PROVIDER] = default_provider;
 
   MigrateOldSettings();
+
+  CollectExceptionNumberUma();
 }
 
 // static
@@ -487,6 +490,26 @@ void HostContentSettingsMap::MigrateOldSettings() {
   }
 }
 
+void HostContentSettingsMap::CollectExceptionNumberUma() {
+  content_settings::ContentSettingsRegistry* registry =
+      content_settings::ContentSettingsRegistry::GetInstance();
+
+  for (const content_settings::ContentSettingsInfo* info : *registry) {

[raymes, 2016/04/12 23:22:39]

If we're just going to record number of exceptions, we might as well do it for
all types in the WebsiteSettingsRegistry :)

[lshang, 2016/04/14 04:55:29]

Done.

+    ContentSettingsType content_type = info->website_settings_info()->type();
+    const std::string type_name = info->website_settings_info()->name();
+
+    ContentSettingsForOneType settings;
+    GetSettingsForOneType(content_type, std::string(), &settings);
+    size_t num_exceptions = 0;
+    for (const ContentSettingPatternSource& setting_entry : settings) {
+      if (setting_entry.source == "preference")
+        ++num_exceptions;
+    }
+    UMA_HISTOGRAM_COUNTS("ContentSettings.NumberOf" + type_name + "Exceptions",

[raymes, 2016/04/12 23:22:39]

I think a more standard naming convention would be something like:
ContentSettings.NumberOfExceptions.<type>

[lshang, 2016/04/14 04:55:29]

Done.

+                         num_exceptions);
+  }
+}
+
 ContentSetting HostContentSettingsMap::GetContentSettingAndMaybeUpdateLastUsage(
     const GURL& primary_url,
     const GURL& secondary_url,