Add histogram to track number of .nexe launches, normalized against opening n...

base/metrics/nacl_histogram.h

Index: base/metrics/nacl_histogram.h
===================================================================
--- base/metrics/nacl_histogram.h	(revision 0)
+++ base/metrics/nacl_histogram.h	(revision 0)
@@ -0,0 +1,29 @@
+// Copyright (c) 2010 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
+
+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|
+void UmaNaclHistogramEnumeration(NaClHistogramValue histogram_value);
+
+#endif  // BASE_METRICS_NACL_HISTOGRAM_H_
+