Histogram the scheme of an origin on the 1st navigation to it.

chrome/browser/profiles/profile_io_data.h

Index: chrome/browser/profiles/profile_io_data.h
diff --git a/chrome/browser/profiles/profile_io_data.h b/chrome/browser/profiles/profile_io_data.h
index 15166f29307b0a3896d8c16fcbc5b141ef853ea8..e79fc8eddd1d954a3bf7631260b7d0599cb8f602 100644
--- a/chrome/browser/profiles/profile_io_data.h
+++ b/chrome/browser/profiles/profile_io_data.h
@@ -8,6 +8,7 @@
 #include <stdint.h>
 
 #include <map>
+#include <set>
 #include <string>
 #include <vector>
 
@@ -204,6 +205,10 @@ class ProfileIOData {
 
   bool IsOffTheRecord() const;
 
+  // Used when deciding whether or not to record
+  // Navigation.SchemePerUniqueOrigin[OTR]. Uses |origins_seen_|.
+  bool HaveAlreadySeenOrigin(const url::Origin& origin);
+
   IntegerPrefMember* incognito_availibility() const {
     return &incognito_availibility_pref_;
   }
@@ -597,6 +602,9 @@ class ProfileIOData {
 
   const Profile::ProfileType profile_type_;
 
+  // Used by |HaveAlreadySeenOrigin|.
+  std::set<url::Origin> origins_seen_;
+
   DISALLOW_COPY_AND_ASSIGN(ProfileIOData);
 };