Remove some unused history resources on iOS

ios/chrome/browser/ui/webui/history/metrics_handler.h

-// 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.
-
-#ifndef IOS_CHROME_BROWSER_UI_WEBUI_HISTORY_METRICS_HANDLER_H_
-#define IOS_CHROME_BROWSER_UI_WEBUI_HISTORY_METRICS_HANDLER_H_
-
-#include "base/compiler_specific.h"
-#include "base/macros.h"
-#include "ios/web/public/webui/web_ui_ios_message_handler.h"
-
-///////////////////////////////////////////////////////////////////////////////
-// MetricsHandler
-
-// Let the page contents record UMA actions. Only use when you can't do it from
-// C++. For example, we currently use it to let the NTP log the position of the
-// Most Visited or Bookmark the user clicked on, as we don't get that
-// information through RequestOpenURL. You will need to update the metrics
-// dashboard with the action names you use, as our processor won't catch that
-// information (treat it as RecordComputedMetrics)
-
-namespace base {
-class ListValue;
-}
-
-class MetricsHandler : public web::WebUIIOSMessageHandler {
- public:
-  MetricsHandler();
-  ~MetricsHandler() override;
-
-  // WebUIIOSMessageHandler implementation.
-  void RegisterMessages() override;
-
-  // Callback for the "metricsHandler:recordAction" message. This records a
-  // user action.
-  void HandleRecordAction(const base::ListValue* args);
-
-  // TODO(dbeam): http://crbug.com/104338
-
-  // Callback for the "metricsHandler:recordInHistogram" message. This records
-  // into a histogram. |args| contains the histogram name, the value to record,
-  // and the maximum allowed value, which can be at most 4000. The histogram
-  // will use at most 100 buckets, one for each 1, 10, or 100 different values,
-  // depending on the maximum value.
-  void HandleRecordInHistogram(const base::ListValue* args);
-
- private:
-  DISALLOW_COPY_AND_ASSIGN(MetricsHandler);
-};
-
-#endif  // IOS_CHROME_BROWSER_UI_WEBUI_HISTORY_METRICS_HANDLER_H_