Bug 1881773 - Collect timezone. r=tjr

Differential Revision: https://phabricator.services.mozilla.com/D202598

toolkit/components/resistfingerprinting/metrics.yaml

@@ -318,3 +318,21 @@ characteristics:
     expires: never
     data_sensitivity:
       - technical
+
+  timezone:
+    type: string
+    description: >
+      The the current timezone of the system
+    lifetime: application
+    send_in_pings:
+      - user-characteristics
+    notification_emails:
+      - tom@mozilla.com
+    bugs:
+      - https://bugzilla.mozilla.org/show_bug.cgi?id=1879151
+      - https://bugzilla.mozilla.org/show_bug.cgi?id=1881773
+    data_reviews:
+      - https://bugzilla.mozilla.org/show_bug.cgi?id=1881773#c4
+    expires: never
+    data_sensitivity:
+      - interaction

toolkit/components/resistfingerprinting/nsUserCharacteristics.cpp

@@ -18,6 +18,7 @@
 #include "mozilla/RelativeLuminanceUtils.h"
 #include "mozilla/ServoStyleConsts.h"
 #include "mozilla/dom/ScreenBinding.h"
+#include "mozilla/intl/TimeZone.h"
 #include "mozilla/widget/ScreenManager.h"
 
 #include "gfxPlatformFontList.h"
@@ -252,6 +253,16 @@ nsresult nsUserCharacteristics::PopulateData(bool aTesting /* = false */) {
   }
   mozilla::glean::characteristics::processor_count.Set(processorCount);
 
+  AutoTArray<char16_t, 128> tzBuffer;
+  auto result = mozilla::intl::TimeZone::GetDefaultTimeZone(tzBuffer);
+  if (result.isOk()) {
+    NS_ConvertUTF16toUTF8 timeZone(
+        nsDependentString(tzBuffer.Elements(), tzBuffer.Length()));
+    mozilla::glean::characteristics::timezone.Set(timeZone);
+  } else {
+    mozilla::glean::characteristics::timezone.Set("<error>"_ns);
+  }
+
   return NS_OK;
 }