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

chrome/browser/tab_contents/origins_seen_service.cc

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/tab_contents/origins_seen_service.h"
+
+namespace {
+const size_t kDefaultMRUCacheSize = 1000;
+}  // namespace
+
+OriginsSeenService::OriginsSeenService()
+    : origins_seen_(kDefaultMRUCacheSize) {}
+
+OriginsSeenService::~OriginsSeenService() {}
+
+bool OriginsSeenService::Insert(const url::Origin& origin) {
+  bool seen = origins_seen_.Peek(origin) != origins_seen_.end();
+  origins_seen_.Put(origin, true);
+  return seen;
+}