Remove NaCl.Startups histogram, this data is tracked in the NaCl plugin now

base/metrics/nacl_histogram.h

-// Copyright (c) 2011 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.
-
-// nacl_histogram provides an enum and defines a macro that uses definitions
-// from histogram.h. Note that a histogram is an object that aggregates
-// statistics, and can summarize them in various forms, including ASCII
-// graphical, HTML, and numerically.
-// nacl_histogram information is used to compare how many times a native
-// client module has been loaded, compared to the number of chrome starts
-// and number of new tabs created.
-
-#ifndef BASE_METRICS_NACL_HISTOGRAM_H_
-#define BASE_METRICS_NACL_HISTOGRAM_H_
-#pragma once
-
-#include "base/base_api.h"
-
-enum NaClHistogramValue {
-  FIRST_TAB_NACL_BASELINE,   // First tab created - a baseline for NaCl starts.
-  NEW_TAB_NACL_BASELINE,     // New tab created -- a baseline for NaCl starts.
-  NACL_STARTED,              // NaCl process started
-  NACL_MAX_HISTOGRAM         // DO NOT USE -- used by histogram for max bound.
-};
-
-// To log histogram data about NaCl.Startups, call this macro with
-// a NaClHistogramValue passed in as |histogram_value|
-BASE_API void UmaNaclHistogramEnumeration(NaClHistogramValue histogram_value);
-
-#endif  // BASE_METRICS_NACL_HISTOGRAM_H_
-