[translate] Add translate ranker model loader.

ios/chrome/browser/translate/translate_ranker_metrics_provider.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 "ios/chrome/browser/translate/translate_ranker_metrics_provider.h"
+
+#include "components/metrics/proto/chrome_user_metrics_extension.pb.h"
+#include "components/metrics/proto/translate_event.pb.h"
+#include "components/translate/core/browser/translate_ranker.h"
+#include "ios/chrome/browser/application_context.h"
+#include "ios/chrome/browser/browser_state/chrome_browser_state.h"
+#include "ios/chrome/browser/browser_state/chrome_browser_state_manager.h"
+#include "ios/chrome/browser/translate/translate_ranker_factory.h"
+#include "ios/web/public/browser_state.h"
+
+namespace translate {
+
+void TranslateRankerMetricsProvider::ProvideGeneralMetrics(
+    metrics::ChromeUserMetricsExtension* uma_proto) {
+  std::vector<ios::ChromeBrowserState*> browser_states =
+      GetApplicationContext()
+          ->GetChromeBrowserStateManager()
+          ->GetLoadedBrowserStates();
+  for (auto* state : browser_states) {
+    TranslateRanker* ranker =
+        TranslateRankerFactory::GetInstance()->GetForBrowserState(state);

[sdefresne, 2017/02/27 21:27:18]

TranslateRankerFactory::GetForBrowserState() cannot return null (as the class
does not override ServiceIsNULLWhileTesting, and uses the non-incognito
BrowserState if the current BrowserState is incognito). So either remove the
null pointer check or add, implement and call GetForBrowserStateIfExists().

[Roger McFarlane (Chromium), 2017/02/27 21:58:33]

Done (switched the check to a DCHECK).

+    if (!ranker)
+      continue;
+
+    std::vector<metrics::TranslateEventProto> translate_events;
+    ranker->FlushTranslateEvents(&translate_events);
+
+    for (auto& event : translate_events) {
+      uma_proto->add_translate_event()->Swap(&event);
+    }
+  }
+}
+
+}  // namespace translate